• Mysql：8.0.19：新特性、过期、已经删除的

    1.4 What Is New in MySQL 8.0
    1.5 Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 8.0

    1.4 What Is New in MySQL 8.0

    This section summarizes what has been added to, deprecated in, and removed from MySQL 8.0. A companion section lists MySQL server options and variables that have been added, deprecated, or removed in MySQL 8.0. See Section 1.5, “Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 8.0”.

    Features Added in MySQL 8.0

    The following features have been added to MySQL 8.0:

    • Data dictionary.  MySQL now incorporates a transactional data dictionary that stores information about database objects. In previous MySQL releases, dictionary data was stored in metadata files and nontransactional tables. For more information, see Chapter 14, MySQL Data Dictionary.

    • Atomic data definition statements (Atomic DDL).  An atomic DDL statement combines the data dictionary updates, storage engine operations, and binary log writes associated with a DDL operation into a single, atomic transaction. For more information, see Section 13.1.1, “Atomic Data Definition Statement Support”.

    • Upgrade procedure.  Previously, after installation of a new version of MySQL, the MySQL server automatically upgrades the data dictionary tables at the next startup, after which the DBA is expected to invoke mysql_upgrade manually to upgrade the system tables in the mysql schema, as well as objects in other schemas such as the sys schema and user schemas.

      As of MySQL 8.0.16, the server performs the tasks previously handled by mysql_upgrade. After installation of a new MySQL version, the server now automatically performs all necessary upgrade tasks at the next startup and is not dependent on the DBA invoking mysql_upgrade. In addition, the server updates the contents of the help tables (something mysql_upgrade did not do). A new --upgrade server option provides control over how the server performs automatic data dictionary and server upgrade operations. For more information, see Section 2.11.3, “What the MySQL Upgrade Process Upgrades”.

    • Security and account management.  These enhancements were added to improve security and enable greater DBA flexibility in account management:

      • The grant tables in the mysql system database are now InnoDB (transactional) tables. Previously, these were MyISAM (nontransactional) tables. The change of grant table storage engine underlies an accompanying change to the behavior of account-management statements. Previously, an account-management statement (such as CREATE USER or DROP USER) that named multiple users could succeed for some users and fail for others. Now, each statement is transactional and either succeeds for all named users or rolls back and has no effect if any error occurs. The statement is written to the binary log if it succeeds, but not if it fails; in that case, rollback occurs and no changes are made. For more information, see Section 13.1.1, “Atomic Data Definition Statement Support”.

      • A new caching_sha2_password authentication plugin is available. Like the sha256_password plugin, caching_sha2_password implements SHA-256 password hashing, but uses caching to address latency issues at connect time. It also supports more connection protocols and does not require linking against OpenSSL for RSA key pair-based password-exchange capabilities. See Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”.

        The caching_sha2_password and sha256_password authentication plugins provide more secure password encryption than the mysql_native_password plugin, and caching_sha2_password provides better performance than sha256_password. Due to these superior security and performance characteristics of caching_sha2_password, it is now the preferred authentication plugin, and is also the default authentication plugin rather than mysql_native_password. For information about the implications of this change of default plugin for server operation and compatibility of the server with clients and connectors, see caching_sha2_password as the Preferred Authentication Plugin.

      • MySQL now supports roles, which are named collections of privileges. Roles can be created and dropped. Roles can have privileges granted to and revoked from them. Roles can be granted to and revoked from user accounts. The active applicable roles for an account can be selected from among those granted to the account, and can be changed during sessions for that account. For more information, see Section 6.2.10, “Using Roles”.

      • MySQL now incorporates the concept of user account categories, with system and regular users distinguished according to whether they have the SYSTEM_USER privilege. See Section 6.2.11, “Account Categories”.

      • Previously, it was not possible to grant privileges that apply globally except for certain schemas. This is now possible if the partial_revokes system variable is enabled. See Section 6.2.12, “Privilege Restriction Using Partial Revokes”.

      • The GRANT statement has an AS user [WITH ROLE] clause that specifies additional information about the privilege context to use for statement execution. This syntax is visible at the SQL level, although its primary purpose is to enable uniform replication across all nodes of grantor privilege restrictions imposed by partial revokes, by causing those restrictions to appear in the binary log. See Section 13.7.1.6, “GRANT Statement”.

      • MySQL now maintains information about password history, enabling restrictions on reuse of previous passwords. DBAs can require that new passwords not be selected from previous passwords for some number of password changes or period of time. It is possible to establish password-reuse policy globally as well as on a per-account basis.

        It is now possible to require that attempts to change account passwords be verified by specifying the current password to be replaced. This enables DBAs to prevent users from changing password without proving that they know the current password. It is possible to establish password-verification policy globally as well as on a per-account basis.

        Accounts are now permitted to have dual passwords, which enables phased password changes to be performed seamlessly in complex multiple-server systems, without downtime.

        MySQL now enables administrators to configure user accounts such that too many consecutive login failures due to incorrect passwords cause temporary account locking. The required number of failures and the lock time are configurable per account.

        These new capabilities provide DBAs more complete control over password management. For more information, see Section 6.2.15, “Password Management”.

      • MySQL now supports FIPS mode, if compiled using OpenSSL, and an OpenSSL library and FIPS Object Module are available at runtime. FIPS mode imposes conditions on cryptographic operations such as restrictions on acceptable encryption algorithms or requirements for longer key lengths. See Section 6.5, “FIPS Support”.

      • The SSL context the server uses for new connections now is reconfigurable at runtime. This capability may be useful, for example, to avoid restarting a MySQL server that has been running so long that its SSL certificate has expired. See Server-Side Runtime Configuration for Encrypted Connections.

      • OpenSSL 1.1.1 supports the TLS v1.3 protocol for encrypted connections, and MySQL 8.0.16 and higher supports TLS v1.3 as well, if both the server and client are compiled using OpenSSL 1.1.1 or higher. See Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

      • MySQL now sets the access control granted to clients on the named pipe to the minimum necessary for successful communication on Windows. Newer MySQL client software can open named pipe connections without any additional configuration. If older client software cannot be upgraded immediately, the new named_pipe_full_access_group system variable can be used to give a Windows group the necessary permissions to open a named pipe connection. Membership in the full-access group should be restricted and temporary.

    • Resource management.  MySQL now supports creation and management of resource groups, and permits assigning threads running within the server to particular groups so that threads execute according to the resources available to the group. Group attributes enable control over its resources, to enable or restrict resource consumption by threads in the group. DBAs can modify these attributes as appropriate for different workloads. Currently, CPU time is a manageable resource, represented by the concept of “virtual CPU” as a term that includes CPU cores, hyperthreads, hardware threads, and so forth. The server determines at startup how many virtual CPUs are available, and database administrators with appropriate privileges can associate these CPUs with resource groups and assign threads to groups. For more information, see Section 8.12.5, “Resource Groups”.

    • Table encryption management.  Table encryption can now be managed globally by defining and enforcing encryption defaults. The default_table_encryption variable defines an encryption default for newly created schemas and general tablespace. The encryption default for a schema can also be defined using the DEFAULT ENCRYPTION clause when creating a schema. By default, a table inherits the encryption of the schema or general tablespace it is created in. Encryption defaults are enforced by enabling the table_encryption_privilege_check variable. The privilege check occurs when creating or altering a schema or general tablespace with an encryption setting that differs from the default_table_encryption setting, or when creating or altering a table with an encryption setting that differs from the default schema encryption. The TABLE_ENCRYPTION_ADMIN privilege permits overriding default encryption settings when table_encryption_privilege_check is enabled. For more information, see Defining an Encryption Default for Schemas and General Tablespaces.

    • InnoDB enhancements.  These InnoDB enhancements were added:

      • The current maximum auto-increment counter value is written to the redo log each time the value changes, and saved to an engine-private system table on each checkpoint. These changes make the current maximum auto-increment counter value persistent across server restarts. Additionally:

        • A server restart no longer cancels the effect of the AUTO_INCREMENT = N table option. If you initialize the auto-increment counter to a specific value, or if you alter the auto-increment counter value to a larger value, the new value is persisted across server restarts.

        • A server restart immediately following a ROLLBACK operation no longer results in the reuse of auto-increment values that were allocated to the rolled-back transaction.

        • If you modify an AUTO_INCREMENT column value to a value larger than the current maximum auto-increment value (in an UPDATE operation, for example), the new value is persisted, and subsequent INSERT operations allocate auto-increment values starting from the new, larger value.

        For more information, see Section 15.6.1.6, “AUTO_INCREMENT Handling in InnoDB”, and InnoDB AUTO_INCREMENT Counter Initialization.

      • When encountering index tree corruption, InnoDB writes a corruption flag to the redo log, which makes the corruption flag crash safe. InnoDB also writes in-memory corruption flag data to an engine-private system table on each checkpoint. During recovery, InnoDB reads corruption flags from both locations and merges results before marking in-memory table and index objects as corrupt.

      • The InnoDB memcached plugin supports multiple get operations (fetching multiple key-value pairs in a single memcached query) and range queries. See Section 15.20.4, “InnoDB memcached Multiple get and Range Query Support”.

      • A new dynamic variable, innodb_deadlock_detect, may be used to disable deadlock detection. On high concurrency systems, deadlock detection can cause a slowdown when numerous threads wait for the same lock. At times, it may be more efficient to disable deadlock detection and rely on the innodb_lock_wait_timeout setting for transaction rollback when a deadlock occurs.

      • The new INFORMATION_SCHEMA.INNODB_CACHED_INDEXES table reports the number of index pages cached in the InnoDB buffer pool for each index.

      • InnoDB temporary tables are now created in the shared temporary tablespace, ibtmp1.

      • The InnoDB tablespace encryption feature supports encryption of redo log and undo log data. See Redo Log Encryption, and Undo Log Encryption.

      • InnoDB supports NOWAIT and SKIP LOCKED options with SELECT ... FOR SHARE and SELECT ... FOR UPDATE locking read statements. NOWAIT causes the statement to return immediately if a requested row is locked by another transaction. SKIP LOCKED removes locked rows from the result set. See Locking Read Concurrency with NOWAIT and SKIP LOCKED.

        SELECT ... FOR SHARE replaces SELECT ... LOCK IN SHARE MODE, but LOCK IN SHARE MODE remains available for backward compatibility. The statements are equivalent. However, FOR UPDATE and FOR SHARE support NOWAIT, SKIP LOCKED, and OF tbl_name options. See Section 13.2.10, “SELECT Statement”.

        OF tbl_name applies locking queries to named tables.

      • ADD PARTITION, DROP PARTITION, COALESCE PARTITION, REORGANIZE PARTITION, and REBUILD PARTITION ALTER TABLE options are supported by native partitioning in-place APIs and may be used with ALGORITHM={COPY|INPLACE} and LOCK clauses.

        DROP PARTITION with ALGORITHM=INPLACE deletes data stored in the partition and drops the partition. However, DROP PARTITION with ALGORITHM=COPY or old_alter_table=ON rebuilds the partitioned table and attempts to move data from the dropped partition to another partition with a compatible PARTITION ... VALUES definition. Data that cannot be moved to another partition is deleted.

      • The InnoDB storage engine now uses the MySQL data dictionary rather than its own storage engine-specific data dictionary. For information about the data dictionary, see Chapter 14, MySQL Data Dictionary.

      • mysql system tables and data dictionary tables are now created in a single InnoDB tablespace file named mysql.ibd in the MySQL data directory. Previously, these tables were created in individual InnoDB tablespace files in the mysql database directory.

      • The following undo tablespace changes are introduced in MySQL 8.0:

        • By default, undo logs now reside in two undo tablespaces that are created when the MySQL instance is initialized. Undo logs are no longer created in the system tablespace.

        • As of MySQL 8.0.14, additional undo tablespaces can be created in a chosen location at runtime using CREATE UNDO TABLESPACE syntax.

          CREATE UNDO TABLESPACE tablespace_name ADD DATAFILE 'file_name.ibu';

          Undo tablespaces created using CREATE UNDO TABLESPACE syntax can be dropped at runtime using DROP UNDO TABLESPACE syntax.

          DROP UNDO TABLESPACE tablespace_name;

          ALTER UNDO TABLESPACE syntax can be used to mark an undo tablespace as active or inactive.

          ALTER UNDO TABLESPACE tablespace_name SET {ACTIVE|INACTIVE};

          A STATE column that shows the state of a tablespace was added to the INFORMATION_SCHEMA.INNODB_TABLESPACES table. An undo tablespace must be in an empty state before it can be dropped.

        • The innodb_undo_log_truncate variable is enabled by default.

        • The innodb_rollback_segments variable defines the number of rollback segments per undo tablespace. Previously, innodb_rollback_segments specified the total number of rollback segments for the MySQL instance. This change increases the number of rollback segments available for concurrent transactions. More rollback segments increases the likelihood that concurrent transactions use separate rollback segments for undo logs, resulting in less resource contention.

      • Default values for variables that affect buffer pool preflushing and flushing behavior were modified:

        • The innodb_max_dirty_pages_pct_lwm default value is now 10. The previous default value of 0 disables buffer pool preflushing. A value of 10 enables preflushing when the percentage of dirty pages in the buffer pool exceeds 10%. Enabling preflushing improves performance consistency.

        • The innodb_max_dirty_pages_pct default value was increased from 75 to 90. InnoDB attempts to flush data from the buffer pool so that the percentage of dirty pages does not exceed this value. The increased default value permits a greater percentage of dirty pages in the buffer pool.

      • The default innodb_autoinc_lock_mode setting is now 2 (interleaved). Interleaved lock mode permits the execution of multi-row inserts in parallel, which improves concurrency and scalability. The new innodb_autoinc_lock_mode default setting reflects the change from statement-based replication to row based replication as the default replication type in MySQL 5.7. Statement-based replication requires the consecutive auto-increment lock mode (the previous default) to ensure that auto-increment values are assigned in a predictable and repeatable order for a given sequence of SQL statements, whereas row-based replication is not sensitive to the execution order of SQL statements. For more information, see InnoDB AUTO_INCREMENT Lock Modes.

        For systems that use statement-based replication, the new innodb_autoinc_lock_mode default setting may break applications that depend on sequential auto-increment values. To restore the previous default, set innodb_autoinc_lock_mode to 1.

      • Renaming a general tablespace is supported by ALTER TABLESPACE ... RENAME TO syntax.

      • The new innodb_dedicated_server variable, which is disabled by default, can be used to have InnoDB automatically configure the following options according to the amount of memory detected on the server:

        This option is intended for MySQL server instances that run on a dedicated server. For more information, see Section 15.8.12, “Enabling Automatic Configuration for a Dedicated MySQL Server”.

      • The new INFORMATION_SCHEMA.INNODB_TABLESPACES_BRIEF view provides space, name, path, flag, and space type data for InnoDB tablespaces.

      • The zlib library version bundled with MySQL was raised from version 1.2.3 to version 1.2.11. MySQL implements compression with the help of the zlib library.

        If you use InnoDB compressed tables, see Section 2.11.4, “Changes in MySQL 8.0” for related upgrade implications.

      • Serialized dictionary information (SDI) is present in all InnoDB tablespace files except for global temporary tablespace and undo tablespace files. SDI is serialized metadata for table and tablespace objects. The presence of SDI data provides metadata redundancy. For example, dictionary object metadata may be extracted from tablespace files if the data dictionary becomes unavailable. SDI extraction is performed using the ibd2sdi tool. SDI data is stored in JSON format.

        The inclusion of SDI data in tablespace files increases tablespace file size. An SDI record requires a single index page, which is 16KB in size by default. However, SDI data is compressed when it is stored to reduce the storage footprint.

      • The InnoDB storage engine now supports atomic DDL, which ensures that DDL operations are either fully committed or rolled back, even if the server halts during the operation. For more information, see Section 13.1.1, “Atomic Data Definition Statement Support”.

      • Tablespace files can be moved or restored to a new location while the server is offline using the innodb_directories option. For more information, see Section 15.6.3.6, “Moving Tablespace Files While the Server is Offline”.

      • The following redo logging optimizations were implemented:

        • User threads can now write concurrently to the log buffer without synchronizing writes.

        • User threads can now add dirty pages to the flush list in a relaxed order.

        • A dedicated log thread is now responsible for writing the log buffer to the system buffers, flushing system buffers to disk, notifying user threads about written and flushed redo, maintaining the lag required for the relaxed flush list order, and write checkpoints.

        • System variables were added for configuring the use of spin delay by user threads waiting for flushed redo:

        • The innodb_log_buffer_size variable is now dynamic, which permits resizing of the log buffer while the server is running.

        For more information, see Section 8.5.4, “Optimizing InnoDB Redo Logging”.

      • As of MySQL 8.0.12, undo logging is supported for small updates to large object (LOB) data, which improves performance of LOB updates that are 100 bytes in size or less. Previously, LOB updates were a minimum of one LOB page in size, which is less than optimal for updates that might only modify a few bytes. This enhancement builds upon support added in MySQL 8.0.4 for partial update of LOB data.

      • As of MySQL 8.0.12, ALGORITHM=INSTANT is supported for the following ALTER TABLE operations:

        • Adding a column. This feature is also referred to as “Instant ADD COLUMN”. Limitations apply. See Section 15.12.1, “Online DDL Operations”.

        • Adding or dropping a virtual column.

        • Adding or dropping a column default value.

        • Modifying the definition of an ENUM or SET column.

        • Changing the index type.

        • Renaming a table.

        Operations that support ALGORITHM=INSTANT only modify metadata in the data dictionary. No metadata locks are taken on the table, and table data is unaffected, making the operations instantaneous. If not specified explicitly, ALGORITHM=INSTANT is used by default by operations that support it. If ALGORITHM=INSTANT is specified but not supported, the operation fails immediately with an error.

        For more information about operations that support ALGORITHM=INSTANT, see Section 15.12.1, “Online DDL Operations”.

      • As of MySQL 8.0.13, the TempTable storage engine supports storage of binary large object (BLOB) type columns. This enhancement improves performance for queries that use temporary tables containing BLOB data. Previously, temporary tables that contained BLOB data were stored in the on-disk storage engine defined by internal_tmp_disk_storage_engine. For more information, see Section 8.4.4, “Internal Temporary Table Use in MySQL”.

      • As of MySQL 8.0.13, the InnoDB data-at-rest encryption feature supports general tablespaces. Previously, only file-per-table tablespaces could be encrypted. To support encryption of general tablespaces, CREATE TABLESPACE and ALTER TABLESPACE syntax was extended to include an ENCRYPTION clause.

        The INFORMATION_SCHEMA.INNODB_TABLESPACES table now includes an ENCRYPTION column that indicates whether or not a tablespace is encrypted.

        The stage/innodb/alter tablespace (encryption) Performance Schema stage instrument was added to permit monitoring of general tablespace encryption operations.

      • Disabling the innodb_buffer_pool_in_core_file variable reduces the size of core files by excluding InnoDB buffer pool pages. To use this variable, the core_file variable must be enabled and the operating system must support the MADV_DONTDUMP non-POSIX extension to madvise(), which is supported in Linux 3.4 and later. For more information, see Section 15.8.3.7, “Excluding Buffer Pool Pages from Core Files”.

      • As of MySQL 8.0.13, user-created temporary tables and internal temporary tables created by the optimizer are stored in session temporary tablespaces that are allocated to a session from a pool of temporary tablespaces. When a session disconnects, its temporary tablespaces are truncated and released back to the pool. In previous releases, temporary tables were created in the global temporary tablespace (ibtmp1), which did not return disk space to the operating system after temporary tables were dropped.

        The innodb_temp_tablespaces_dir variable defines the location where session temporary tablespaces are created. The default location is the #innodb_temp directory in the data directory.

        The INNODB_SESSION_TEMP_TABLESPACES table provides metadata about session temporary tablespaces.

        The global temporary tablespace (ibtmp1) now stores rollback segments for changes made to user-created temporary tables.

      • As of MySQL 8.0.14, InnoDB supports parallel clustered index reads, which can improve CHECK TABLE performance. This feature does not apply to secondary index scans. The innodb_parallel_read_threads session variable must be set to a value greater than 1 for parallel clustered index reads to occur. The default value is 4. The actual number of threads used to perform a parallel clustered index read is determined by the innodb_parallel_read_threads setting or the number of index subtrees to scan, whichever is smaller.

      • As of 8.0.14, when the innodb_dedicated_server variable is enabled, the size and number of log files are configured according to the automatically configured buffer pool size. Previously, log file size was configured according to the amount of memory detected on the server, and the number of log files was not configured automatically.

      • As of 8.0.14, the ADD DATAFILE clause of the CREATE TABLESPACE statement is optional, which permits users without the FILE privilege to create tablespaces. A CREATE TABLESPACE statement executed without an ADD DATAFILE clause implicitly creates a tablespace data file with a unique file name.

      • By default, when the amount of memory occupied by the TempTable storage engine exceeds the memory limit defined by the temptable_max_ram variable, the TempTable storage engine begins allocating memory-mapped temporary files from disk. As of MySQL 8.0.16, this behavior is controlled by the temptable_use_mmap variable. Disabling temptable_use_mmap causes the TempTable storage engine to use InnoDB on-disk internal temporary tables instead of memory-mapped files as its overflow mechanism. For more information, see Internal Temporary Table Storage Engine.

      • As of MySQL 8.0.16, the InnoDB data-at-rest encryption feature supports encryption of the mysql system tablespace. The mysql system tablespace contains the mysql system database and the MySQL data dictionary tables. For more information, see Section 15.13, “InnoDB Data-at-Rest Encryption”.

      • The innodb_spin_wait_pause_multiplier variable, introduced in MySQL 8.0.16, provides greater control over the duration of spin-lock polling delays that occur when a thread waits to acquire a mutex or rw-lock. Delays can be tuned more finely to account for differences in PAUSE instruction duration on different processor architectures. For more information, see Section 15.8.8, “Configuring Spin Lock Polling”.

      • InnoDB parallel read thread performance for large data sets was improved in MySQL 8.0.17 through better utilization of read threads, through a reduction in read thread I/O for prefetch activity that occurs during parallel scans, and through support for parallel scanning of partitions.

        The parallel read thread feature is controlled by the innodb_parallel_read_threads variable. The maximum setting is now 256, which is the total number of threads for all client connections. If the thread limit is reached, connections fall back to using a single thread.

      • The innodb_idle_flush_pct variable, introduced in MySQL 8.0.18, permits placing a limit on page flushing during idle periods, which can help extend the life of solid state storage devices. See Limiting Buffer Flushing During Idle Periods.

      • Support was added for efficient sampling of InnoDB data for the purpose of generating histogram statistics. See Histogram Statistics Analysis.

    • Character set support.  The default character set has changed from latin1 to utf8mb4. The utf8mb4 character set has several new collations, including utf8mb4_ja_0900_as_cs, the first Japanese language-specific collation available for Unicode in MySQL. For more information, see Section 10.10.1, “Unicode Character Sets”.

    • JSON enhancements.  The following enhancements or additions were made to MySQL's JSON functionality:

      • Added the ->> (inline path) operator, which is equivalent to calling JSON_UNQUOTE() on the result of JSON_EXTRACT().

        This is a refinement of the column path operator -> introduced in MySQL 5.7; col->>"$.path" is equivalent to JSON_UNQUOTE(col->"$.path"). The inline path operator can be used wherever you can use JSON_UNQUOTE(JSON_EXTRACT()), such SELECT column lists, WHERE and HAVING clauses, and ORDER BY and GROUP BY clauses. For more information, see the description of the operator, as well as JSON Path Syntax.

      • Added two JSON aggregation functions JSON_ARRAYAGG() and JSON_OBJECTAGG(). JSON_ARRAYAGG() takes a column or expression as its argument, and aggregates the result as a single JSON array. The expression can evaluate to any MySQL data type; this does not have to be a JSON value. JSON_OBJECTAGG() takes two columns or expressions which it interprets as a key and a value; it returns the result as a single JSON object. For more information and examples, see Section 12.20, “Aggregate (GROUP BY) Functions”.

      • Added the JSON utility function JSON_PRETTY(), which outputs an existing JSON value in an easy-to-read format; each JSON object member or array value is printed on a separate line, and a child object or array is intended 2 spaces with respect to its parent.

        This function also works with a string that can be parsed as a JSON value.

        For more detailed information and examples, see Section 12.17.8, “JSON Utility Functions”.

      • When sorting JSON values in a query using ORDER BY, each value is now represented by a variable-length part of the sort key, rather than a part of a fixed 1K in size. In many cases this can reduce excessive usage. For example, a scalar INT or even BIGINT value actually requires very few bytes, so that the remainder of this space (up to 90% or more) was taken up by padding. This change has the following benefits for performance:

        • Sort buffer space is now used more effectively, so that filesorts need not flush to disk as early or often as with fixed-length sort keys. This means that more data can be sorted in memory, avoiding unnecessary disk access.

        • Shorter keys can be compared more quickly than longer ones, providing a noticeable improvement in performance. This is true for sorts performed entirely in memory as well as for sorts that require writing to and reading from disk.

      • Added support in MySQL 8.0.2 for partial, in-place updates of JSON column values, which is more efficient than completely removing an existing JSON value and writing a new one in its place, as was done previously when updating any JSON column. For this optimization to be applied, the update must be applied using JSON_SET(), JSON_REPLACE(), or JSON_REMOVE(). New elements cannot be added to the JSON document being updated; values within the document cannot take more space than they did before the update. See Partial Updates of JSON Values, for a detailed discussion of the requirements.

        Partial updates of JSON documents can be written to the binary log, taking up less space than logging complete JSON documents. Partial updates are always logged as such when statement-based replication is in use. For this to work with row-based replication, you must first set binlog_row_value_options=PARTIAL_JSON; see this variable's description for more information.

      • Added the JSON utility functions JSON_STORAGE_SIZE() and JSON_STORAGE_FREE(). JSON_STORAGE_SIZE() returns the storage space in bytes used for the binary representation of a JSON document prior to any partial update (see previous item). JSON_STORAGE_FREE() shows the amount of space remaining in a table column of type JSON after it has been partially updated using JSON_SET() or JSON_REPLACE(); this is greater than zero if the binary representation of the new value is less than that of the previous value.

        Each of these functions also accepts a valid string representation of a JSON document. For such a value, JSON_STORAGE_SIZE() returns the space used by its binary representation following its conversion to a JSON document. For a variable containing the string representation of a JSON document, JSON_STORAGE_FREE() returns zero. Either function produces an error if its (non-null) argument cannot be parsed as a valid JSON document, and NULL if the argument is NULL.

        For more information and examples, see Section 12.17.8, “JSON Utility Functions”.

        JSON_STORAGE_SIZE() and JSON_STORAGE_FREE() were implemented in MySQL 8.0.2.

      • Added support in MySQL 8.0.2 for ranges such as $[1 to 5] in XPath expressions. Also added support in this version for the last keyword and relative addressing, such that $[last] always selects the last (highest-numbered) element in the array and $[last-1] the next to last element. last and expressions using it can also be included in range definitions. For example, $[last-2 to last-1] returns the last two elements but one from an array. See Searching and Modifying JSON Values, for additional information and examples.

      • Added a JSON merge function intended to conform to RFC 7396. JSON_MERGE_PATCH(), when used on 2 JSON objects, merges them into a single JSON object that has as members a union of the following sets:

        • Each member of the first object for which there is no member with the same key in the second object.

        • Each member of the second object for which there is no member having the same key in the first object, and whose value is not the JSON null literal.

        • Each member having a key that exists in both objects, and whose value in the second object is not the JSON null literal.

        As part of this work, the JSON_MERGE() function has been renamed JSON_MERGE_PRESERVE(). JSON_MERGE() continues to be recognized as an alias for JSON_MERGE_PRESERVE() in MySQL 8.0, but is now deprecated and is subject to removal in a future version of MySQL.

        For more information and examples, see Section 12.17.4, “Functions That Modify JSON Values”.

      • Implemented “last duplicate key wins” normalization of duplicate keys, consistent with RFC 7159 and most JavaScript parsers. An example of this behavior is shown here, where only the rightmost member having the key x is preserved: 

        mysql> SELECT JSON_OBJECT('x', '32', 'y', '[true, false]',
     >                     'x', '"abc"', 'x', '100') AS Result;
+------------------------------------+
| Result                             |
+------------------------------------+
| {"x": "100", "y": "[true, false]"} |
+------------------------------------+
1 row in set (0.00 sec)

        Values inserted into MySQL JSON columns are also normalized in this way, as shown in this example:

        mysql> CREATE TABLE t1 (c1 JSON);

mysql> INSERT INTO t1 VALUES ('{"x": 17, "x": "red", "x": [3, 5, 7]}');

mysql> SELECT c1 FROM t1;
+------------------+
| c1               |
+------------------+
| {"x": [3, 5, 7]} |
+------------------+

        This is an incompatible change from previous versions of MySQL, where a “first duplicate key wins” algorithm was used in such cases.

        See Normalization, Merging, and Autowrapping of JSON Values, for more information and examples.

      • Added the JSON_TABLE() function in MySQL 8.0.4. This function accepts JSON data and returns it as a relational table having the specified columns.

        This function has the syntax JSON_TABLE(expr, path COLUMNS column_list) [AS] alias), where expr is an expression that returns JSON data, path is a JSON path applied to the source, and column_list is a list of column definitions. An example is shown here:

        mysql> SELECT *
    -> FROM
    ->   JSON_TABLE(
    ->     '[{"a":3,"b":"0"},{"a":"3","b":"1"},{"a":2,"b":1},{"a":0},{"b":[1,2]}]',
    ->     "$[*]" COLUMNS(
    ->       rowid FOR ORDINALITY,
    ->
    ->       xa INT EXISTS PATH "$.a",
    ->       xb INT EXISTS PATH "$.b",
    ->
    ->       sa VARCHAR(100) PATH "$.a",
    ->       sb VARCHAR(100) PATH "$.b",
    ->
    ->       ja JSON PATH "$.a",
    ->       jb JSON PATH "$.b"
    ->     )
    ->   ) AS  jt1;
+-------+------+------+------+------+------+--------+
| rowid | xa   | xb   | sa   | sb   | ja   | jb     |
+-------+------+------+------+------+------+--------+
|     1 |    1 |    1 | 3    | 0    | 3    | "0"    |
|     2 |    1 |    1 | 3    | 1    | "3"  | "1"    |
|     3 |    1 |    1 | 2    | 1    | 2    | 1      |
|     4 |    1 |    0 | 0    | NULL | 0    | NULL   |
|     5 |    0 |    1 | NULL | NULL | NULL | [1, 2] |
+-------+------+------+------+------+------+--------+

        The JSON source expression can be any expression that yields a valid JSON document, including a JSON literal, a table column, or a function call that returns JSON such as JSON_EXTRACT(t1, data, '$.post.comments'). For more information, see Section 12.17.6, “JSON Table Functions”.

    • Data type support.  MySQL now supports use of expressions as default values in data type specifications. This includes the use of expressions as default values for the BLOB, TEXT, GEOMETRY, and JSON data types, which previously could not be assigned default values at all. For details, see Section 11.6, “Data Type Default Values”.

    • Optimizer.  These optimizer enhancements were added:

      • MySQL now supports invisible indexes. An invisible index is not used by the optimizer at all, but is otherwise maintained normally. Indexes are visible by default. Invisible indexes make it possible to test the effect of removing an index on query performance, without making a destructive change that must be undone should the index turn out to be required. See Section 8.3.12, “Invisible Indexes”.

      • MySQL now supports descending indexes: DESC in an index definition is no longer ignored but causes storage of key values in descending order. Previously, indexes could be scanned in reverse order but at a performance penalty. A descending index can be scanned in forward order, which is more efficient. Descending indexes also make it possible for the optimizer to use multiple-column indexes when the most efficient scan order mixes ascending order for some columns and descending order for others. See Section 8.3.13, “Descending Indexes”.

      • MySQL now supports creation of functional index key parts that index expression values rather than column values. Functional key parts enable indexing of values that cannot be indexed otherwise, such as JSON values. For details, see Section 13.1.15, “CREATE INDEX Statement”.

      • In MySQL 8.0.14 and later, trivial WHERE conditions arising from constant literal expressions are removed during preparation, rather than later on during optimization. Removal of the condition earlier in the process makes it possible to simplify joins for queries with outer joins having trivial conditions, such as this one:

        SELECT * FROM t1 LEFT JOIN t2 ON condition_1 WHERE condition_2 OR 0 = 1

        The optimizer now sees during preparation that 0 = 1 is always false, making OR 0 = 1 redundant, and removes it, leaving this:

        SELECT * FROM t1 LEFT JOIN t2 ON condition_1 where condition_2

        Now the optimizer can rewrite the query as an inner join, like this:

        SELECT * FROM t1 LEFT JOIN t2 WHERE condition_1 AND condition_2

        For more information, see Section 8.2.1.9, “Outer Join Optimization”.

      • In MySQL 8.0.16 and later, MySQL can use constant folding at optimization time to handle comparisons between a column and a constant value where the constant is out of range or on a range boundary with respect to the type of the column, rather than doing so for each row at execution time. For example, given a table t with a TINYINT UNSIGNED column c, the optimizer can rewrite a condition such as WHERE c < 256 to WHERE 1 (and optimize the condition away altogether), or WHERE c >= 255 to WHERE c = 255.

        See Section 8.2.1.14, “Constant-Folding Optimization”, for more information.

      • Beginning with MySQL 8.0.16, the semijoin optimizations used with IN subqueries can now be applied to EXISTS subqueries as well. In addition, the optimizer now decorrelates trivially-correlated equality predicates in the WHERE condition attached to the subquery, so that they can be treated similarly to expressions in IN subqueries; this applies to both EXISTS and IN subqueries.

        For more information, see Section 8.2.2.1, “Optimizing IN and EXISTS Subquery Predicates with Semijoin Transformations”.

      • In MySQL 8.0.17 and later a WHERE condition having NOT IN (subquery) or NOT EXISTS (subquery) is transformed internally into an antijoin. (An antijoin returns all rows from the table for which there is no row in the table to which it is joined matching the join condition.) This removes the subquery which can result in faster query execution since the subquery's tables are now handled on the top level.

        This is similar to, and reuses, the existing IS NULL (Not exists) optimization for outer joins; see EXPLAIN Extra Information.

    • Common table expressions.  MySQL now supports common table expressions, both nonrecursive and recursive. Common table expressions enable use of named temporary result sets, implemented by permitting a WITH clause preceding SELECT statements and certain other statements. For more information, see Section 13.2.15, “WITH (Common Table Expressions)”.

      As of MySQL 8.0.19, the recursive SELECT part of a recursive common table expression (CTE) supports a LIMIT clause. LIMIT with OFFSET is also supported. See Recursive Common Table Expressions, for more information.

    • Window functions.  MySQL now supports window functions that, for each row from a query, perform a calculation using rows related to that row. These include functions such as RANK(), LAG(), and NTILE(). In addition, several existing aggregate functions now can be used as window functions (for example, SUM() and AVG()). For more information, see Section 12.21, “Window Functions”.

    • Lateral derived tables.  A derived table now may be preceded by the LATERAL keyword to specify that it is permitted to refer to (depend on) columns of preceding tables in the same FROM clause. Lateral derived tables make possible certain SQL operations that cannot be done with nonlateral derived tables or that require less-efficient workarounds. See Section 13.2.11.9, “Lateral Derived Tables”.

    • Aliases in single-table DELETE statements.  In MySQL 8.0.16 and later, single-table DELETE statements support the use of table aliases.

    • Regular expression support.  Previously, MySQL used the Henry Spencer regular expression library to support regular expression operators (REGEXP, RLIKE). Regular expression support has been reimplemented using International Components for Unicode (ICU), which provides full Unicode support and is multibyte safe. The REGEXP_LIKE() function performs regular expression matching in the manner of the REGEXP and RLIKE operators, which now are synonyms for that function. In addition, the REGEXP_INSTR(), REGEXP_REPLACE(), and REGEXP_SUBSTR() functions are available to find match positions and perform substring substitution and extraction, respectively. The regexp_stack_limit and regexp_time_limit system variables provide control over resource consumption by the match engine. For more information, see Section 12.7.2, “Regular Expressions”. For information about ways in which applications that use regular expressions may be affected by the implementation change, see Regular Expression Compatibility Considerations.

    • Internal temporary tables.  The TempTable storage engine replaces the MEMORY storage engine as the default engine for in-memory internal temporary tables. The TempTable storage engine provides efficient storage for VARCHAR and VARBINARY columns. The internal_tmp_mem_storage_engine session variable defines the storage engine for in-memory internal temporary tables. Permitted values are TempTable (the default) and MEMORY. The temptable_max_ram variable defines the maximum amount of memory that the TempTable storage engine can use before data is stored to disk.

    • Logging.  Error logging was rewritten to use the MySQL component architecture. Traditional error logging is implemented using built-in components, and logging using the system log is implemented as a loadable component. In addition, a loadable JSON log writer is available. To control which log components to enable, use the log_error_services system variable. For more information, see Section 5.4.2, “The Error Log”.

    • Backup lock.  A new type of backup lock permits DML during an online backup while preventing operations that could result in an inconsistent snapshot. The new backup lock is supported by LOCK INSTANCE FOR BACKUP and UNLOCK INSTANCE syntax. The BACKUP_ADMIN privilege is required to use these statements.

    • Replication.  The following enhancements have been made to MySQL Replication:

      • MySQL Replication now supports binary logging of partial updates to JSON documents using a compact binary format, saving space in the log over logging complete JSON documents. Such compact logging is done automatically when statement-based logging is in use, and can be enabled by setting the new binlog_row_value_options system variable to PARTIAL_JSON. For more information, see Partial Updates of JSON Values, as well as the description of binlog_row_value_options.

    • Connection management.  MySQL Server now permits a TCP/IP port to be configured specifically for administrative connections. This provides an alternative to the single administrative connection that is permitted on the network interfaces used for ordinary connections even when max_connections connections are already established. See Section 8.12.4.1, “How MySQL Handles Client Connections”.

      MySQL now provides more control over the use of compression to minimize the number of bytes sent over connections to the server. Previously, a given connection was either uncompressed or used the zlib compression algorithm. Now, it is also possible to use the zstd algorithm, and to select a compression level for zstd connections. The permitted compression algorithms can be configured on the server side, as well as on the connection-origination side for connections by client programs and by servers participating in master/slave replication or Group Replication. For more information, see Section 4.2.6, “Connection Compression Control”.

    • Configuration.  The maximum permitted length of host names throughout MySQL has been raised to 255 ASCII characters, up from the previous limit of 60 characters. This applies to, for example, host name-related columns in the data dictionary, mysql system schema, Performance Schema, INFORMATION_SCHEMA, and sys schema; the MASTER_HOST value for the CHANGE MASTER TO statement; the Host column in SHOW PROCESSLIST statement output; host names in account names (such as used in account-management statements and in DEFINER attributes); and host name-related command options and system variables.

      Caveats:

      • The increase in permitted host name length can affect tables with indexes on host name columns. For example, tables in the mysql system schema that index host names now have an explicit ROW_FORMAT attribute of DYNAMIC to accommodate longer index values.

      • Some file name-valued configuration settings might be constructed based on the server host name. The permitted values are constrained by the underlying operating system, which may not permit file names long enough to include 255-character host names. This affects the general_log_file, log_error, pid_file, relay_log, and slow_query_log_file system variables and corresponding options. If host name-based values are too long for the OS, explicit shorter values must be provided.

      • Although the server now supports 255-character host names, connections to the server established using the --ssl-mode=VERIFY_IDENTITY option are constrained by maximum host name length supported by OpenSSL. Host name matches pertain to two fields of SSL certificates, which have maximum lengths as follows: Common Name: maximum length 64; Subject Alternative Name: maximum length as per RFC#1034.

    • Plugins.  Previously, MySQL plugins could be written in C or C++. MySQL header files used by plugins now contain C++ code, which means that plugins must be written in C++, not C.

    • C API.  The MySQL C API now supports asynchronous functions for nonblocking communication with the MySQL server. Each function is the asynchronous counterpart to an existing synchronous function. The synchronous functions block if reads from or writes to the server connection must wait. The asynchronous functions enable an application to check whether work on the server connection is ready to proceed. If not, the application can perform other work before checking again later. See Section 28.7.11, “C API Asynchronous Interface”.

    • Additional target types for casts.  The functions CAST() and CONVERT() now support conversions to types DOUBLE, FLOAT, and REAL. Added in MySQL 8.0.17. See Section 12.10, “Cast Functions and Operators”.

    • JSON schema validation.  MySQL 8.0.17 adds two functions JSON_SCHEMA_VALID() and JSON_SCHEMA_VALIDATION_REPORT() for validating JSON documents again JSON schemas. JSON_SCHEMA_VALID() returns TRUE (1) if the document validates against the schema and FALSE (0) if it does not. JSON_SCHEMA_VALIDATION_REPORT() returns a JSON document containing detailed information about the results of the validation. The following statements apply to both of these functions:

      • The schema must conform to Draft 4 of the JSON Schema specification.

      • required attributes are supported.

      • External resources and the $ref keyword are not supported.

      • Regular expression patterns are supported; invalid patterns are silently ignored.

      See Section 12.17.7, “JSON Schema Validation Functions”, for more information and examples.

    • Multi-valued indexes.  Beginning with MySQL 8.0.17, InnoDB supports the creation of a multi-valued index, which is a secondary index defined on a JSON column that stores an array of values and which can have multiple index records for a single data record. Such an index uses a key part definition such as CAST(data->'$.zipcode' AS UNSIGNED ARRAY). A multi-valued index is used automatically by the MySQL optimizer for suitable queries, as can be viewed in the output of EXPLAIN.

      As part of this work, MySQL adds a new function JSON_OVERLAPS() and a new MEMBER OF() operator for working with JSON documents, additionally extending the CAST() function with a new ARRAY keyword, as described in the following list:

      • JSON_OVERLAPS() compares two JSON documents. If they contain any key-value pairs or array elements in common, the function returns TRUE (1); otherwise it returns FALSE (0). If both values are scalars, the function performs a simple test for equality. If one argument is a JSON array and the other is a scalar, the scalar is treated as an array element. Thus, JSON_OVERLAPS() acts as a complement to JSON_CONTAINS().

      • MEMBER OF() tests whether the first operand (a scalar or JSON document) is a member of the JSON array passed as the second operand, returning TRUE (1) if it is, and FALSE (0) if it is not. No type conversion of the operand is performed.

      • CAST(expression AS type ARRAY) permits creation of a functional index by casting the JSON array found in a JSON document at json_path to an SQL array. Type specifiers are limited to those already supported by CAST(), with the exception of BINARY (not supported). This usage of CAST() (and the ARRAY keyword) is supported only by InnoDB, and only for the creation of a multi-valued index.

      For detailed information about multi-valued indexes, including examples, see Multi-Valued Indexes. Section 12.17.3, “Functions That Search JSON Values”, provides information about JSON_OVERLAPS() and MEMBER OF(), along with examples of use.

    • Hintable time_zone.  As of MySQL 8.0.17, the time_zone session variable is hintable using SET_VAR.

    • Redo Log Archiving.  As of MySQL 8.0.17, InnoDB supports redo log archiving. Backup utilities that copy redo log records may sometimes fail to keep pace with redo log generation while a backup operation is in progress, resulting in lost redo log records due to those records being overwritten. The redo log archiving feature addresses this issue by sequentially writing redo log records to an archive file. Backup utilities can copy redo log records from the archive file as necessary, thereby avoiding the potential loss of data. For more information, see Redo Log Archiving.

    • The Clone Plugin.  As of MySQL 8.0.17, MySQL provides a clone plugin that permits cloning InnoDB data locally or from a remote MySQL server instance. A local cloning operation stores cloned data on the same server or node where the MySQL instance runs. A remote cloning operation transfers cloned data over the network from a donor MySQL server instance to the recipient server or node where the cloning operation was initiated.

      The clone plugin supports replication. In addition to cloning data, a cloning operation extracts and transfers replication coordinates from the donor and applies them on the recipient, which enables using the clone plugin for provisioning Group Replication members and replication slaves. Using the clone plugin for provisioning is considerably faster and more efficient than replicating a large number of transactions. Group Replication members can also be configured to use the clone plugin as an alternative method of recovery, so that members automatically choose the most efficient way to retrieve group data from seed members.

      For more information, see Section 5.6.7, “The Clone Plugin”, and Section 18.4.3.1, “Cloning for Distributed Recovery”.

    • Hash Join Optimization.  Beginning with MySQL 8.0.18, a hash join is used whenever each pair of tables in a join includes at least one equi-join condition. A hash join does not require indexes, and is more efficient in most cases than the block-nested loop algorithm. Joins such as those shown here can be optimized in this manner:

      SELECT *
    FROM t1
    JOIN t2
        ON t1.c1=t2.c1;

SELECT *
    FROM t1
    JOIN t2
        ON (t1.c1 = t2.c1 AND t1.c2 < t2.c2)
    JOIN t3
        ON (t2.c1 = t3.c1)

      Hash joins can also be used for Cartesian products—that is, when no join condition is specified.

      You can see when the hash join optimization is being used for a particular query using EXPLAIN FORMAT=TREE or EXPLAIN ANALYZE.

      Use of hash joins can be controlled using the optimizer_switch system variable' hash_join flag (on by default) as well as the HASH_JOIN and NO_HASH_JOIN optimizer hints.

      The amount of memory available to a hash join is limited by the value of join_buffer_size. A hash join that requires more than this much memory is executed on disk; the number of disk files that can be used by an on-disk hash join is limited by open_files_limit.

      For more information and examples, see Section 8.2.1.4, “Hash Join Optimization”.

      As of MySQL 8.0.19, the hash_join optimizer switch introduced in MySQL 8.0.18 no longer has any effect. This also applies to the HASH_JOIN and NO_HASH_JOIN optimizer hints. The switch and the hint are both now deprecated and will be removed in a future MySQL release.

    • EXPLAIN ANALYZE Statement.  A new form of the EXPLAIN statement, EXPLAIN ANALYZE, is implemented in MySQL 8.0.18, providing expanded information about the execution of SELECT statements in TREE format for each iterator used in processing the query, and making it possible to compare estimated cost with the actual cost of the query. This information includes startup cost, total cost, number of rows returned by this iterator, and the number of loops executed.

      In MySQL 8.0.20 and later, this statement also supports a FORMAT=TREE specifier. TREE is the only supported format.

      See Obtaining Information with EXPLAIN ANALYZE, for more information.

    • Query cast injection.  In version 8.0.18 and later, MySQL now injects cast operations into the query item tree inside expressions and conditions in which the data type of the argument and the expected data type do not match. This has no effect on query results or speed of execution, but makes the query as executed equivalent to one which is compliant with the SQL standard while maintaining backwards compatibility with previous releases of MySQL.

      Such implicit casts are now performed between temporal types (DATE, DATETIME, TIMESTAMP, TIME) and numeric types (SMALLINT, TINYINT, MEDIUMINT, INT/INTEGER, BIGINT; DECIMAL/NUMERIC; FLOAT, DOUBLE, REAL; BIT) whenever they are compared using any of the standard numeric comparison operators (=, >=, >, <, <=, <>/!=, or <=>). In this case, any value that is not already a DOUBLE is cast as one. Cast injection is also now performed for comparisons between DATE or TIME values and DATETIME values, where the arguments are cast whenever necessary as DATETIME.

      It is possible to see when casts are injected into a given query by viewing the output of EXPLAIN ANALYZE, EXPLAIN FORMAT=JSON, or, as shown here, EXPLAIN FORMAT=TREE:

      mysql> CREATE TABLE d (dt DATETIME, d DATE, t TIME);
Query OK, 0 rows affected (0.62 sec)

mysql> CREATE TABLE n (i INT, d DECIMAL, f FLOAT, dc DECIMAL);
Query OK, 0 rows affected (0.51 sec)

mysql> EXPLAIN FORMAT=TREE SELECT * from d JOIN n ON d.dt = n.iG
*************************** 1. row ***************************
EXPLAIN: -> Inner hash join (cast(d.dt as double) = cast(n.i as double))
(cost=0.70 rows=1)
    -> Table scan on n  (cost=0.35 rows=1)
    -> Hash
        -> Table scan on d  (cost=0.35 rows=1)

      Such casts can also be seen by executing EXPLAIN [FORMAT=TRADITIONAL], in which case it is also necessary to issue SHOW WARNINGS afterwards.

    • Time zone support for TIMESTAMP and DATETIME.  As of MySQL 8.0.19, the server accepts a time zone offset with inserted datetime (TIMESTAMP and DATETIME) values. This offset uses the same format as that employed when setting the time_zone system variable, except that a leading zero is required when the hours portion of the offset is less than 10, and '-00:00' is not allowed. Examples of datetime literals that include time zone offsets are '2019-12-11 10:40:30-05:00', '2003-04-14 03:30:00+10:00', and '2020-01-01 15:35:45+05:30'.

      Time zone offsets are not displayed when selecting datetime values.

      Datetime literals incorporating time zone offsets can be used as prepared statement parameter values.

      As part of this work, the value used to set the time_zone system variable is now also restricted to the range -14:00 to +14:00, inclusive. (It remains possible to assign name values to time_zone such as 'EST', 'Posix/Australia/Brisbane', and 'Europe/Stockholm' to this variable, provided that the MySQL time zone tables are loaded; see Populating the Time Zone Tables).

      For more information and examples, see Section 5.1.13, “MySQL Server Time Zone Support”, as well as Section 11.2.2, “The DATE, DATETIME, and TIMESTAMP Types”.

    • Precise information for JSON schema CHECK constraint failures.  When using JSON_SCHEMA_VALID() to specify a CHECK constraint, MySQL 8.0.19 and later provides precise information about the reasons for failures of such constraints.

      For examples and more information, see JSON_SCHEMA_VALID() and CHECK constraints. See also Section 13.1.20.7, “CHECK Constraints”.

    • Row and column aliases with ON DUPLICATE KEY UPDATE.  Beginning with MySQL 8.0.19, it is possible to reference the row to be inserted, and, optionally, its columns, using aliases. Consider the following INSERT statement on a table t having columns a and b:

      INSERT INTO t SET a=9,b=5
    ON DUPLICATE KEY UPDATE a=VALUES(a)+VALUES(b);

      Using the alias new for the new row, and, in some cases, the aliases m and n for this row's columns, the INSERT statement can be rewritten in many different ways, some examples of which are shown here:

      INSERT INTO t SET a=9,b=5 AS new
    ON DUPLICATE KEY UPDATE a=new.a+new.b;

INSERT INTO t VALUES(9,5) AS new
    ON DUPLICATE KEY UPDATE a=new.a+new.b;

INSERT INTO t SET a=9,b=5 AS new(m,n)
    ON DUPLICATE KEY UPDATE a=m+n;

INSERT INTO t VALUES(9,5) AS new(m,n)
    ON DUPLICATE KEY UPDATE a=m+n;

      For more information and examples, see Section 13.2.6.2, “INSERT ... ON DUPLICATE KEY UPDATE Statement”.

    • SQL standard explicit table clause and table value constructor.  Added table value constructors and explicit table clauses according to the SQL standard. These are implemented in MySQL 8.0.19, respectively, as the TABLE statement and the VALUES statement.

      The TABLE statement has the format TABLE table_name, and is equivalent to SELECT * FROM table_name. It supports ORDER BY and LIMIT clauses ( the latter with optional OFFSET), but does not allow for the selection of individual table columns. TABLE can be used anywhere that you would employ the equivalent SELECT statement; this includes joins, unions, INSERT ... SELECT, REPLACE, CREATE TABLE ... SELECT statements, and subqueries. For example:

      • TABLE t1 UNION TABLE t2 is equivalent to SELECT * FROM t1 UNION SELECT * FROM t2

      • CREATE TABLE t2 TABLE t1 is equivalent to CREATE TABLE t2 SELECT * FROM t1

      • SELECT a FROM t1 WHERE b > ANY (TABLE t2) is equivalent to SELECT a FROM t1 WHERE b > ANY (SELECT * FROM t2).

      VALUES can be used to supply a table value to an INSERT, REPLACE, or SELECT statement, and consists of the VALUES keyword followed by a series of row constructors (ROW()) separated by commas. For example, the statement INSERT INTO t1 VALUES ROW(1,2,3), ROW(4,5,6), ROW(7,8,9) provides an SQL-compliant equivalent to the MySQL-specific INSERT INTO t1 VALUES (1,2,3), (4,5,6), (7,8,9). You can also select from a VALUES table value constructor just as you would a table, bearing in mind that you must supply a table alias when doing so, and use this SELECT just as you would any other; this includes joins, unions, and subqueries.

      For more information about TABLE and VALUES, and for examples of their use, see the following sections of this documentation:

    • Optimizer hints for FORCE INDEX, IGNORE INDEX.  MySQL 8.0 introduces index-level optimizer hints which serve as analogs to the traditional index hints as described in Section 8.9.4, “Index Hints”. The new hints are listed here, along with their FORCE INDEX or IGNORE INDEX equivalents:

      For example, the following two queries are equivalent:

      SELECT a FROM t1 FORCE INDEX (i_a) FOR JOIN WHERE a=1 AND b=2;

SELECT /*+ JOIN_INDEX(t1 i_a) */ a FROM t1 WHERE a=1 AND b=2;

      The optimizer hints listed previously follow the same basic rules for syntax and usage as existing index-level optimizer hints.

      These optimizer hints are intended to replace FORCE INDEX and IGNORE INDEX, which we plan to deprecate in a future MySQL release, and subsequently to remove from MySQL. They do not implement a single exact equivalent for USE INDEX; instead, you can employ one or more of NO_INDEX, NO_JOIN_INDEX, NO_GROUP_INDEX, or NO_ORDER_INDEX to achieve the same effect.

      For further information and examples of use, see Index-Level Optimizer Hints.

    Features Deprecated in MySQL 8.0

    The following features are deprecated in MySQL 8.0 and may be or will be removed in a future series. Where alternatives are shown, applications should be updated to use them.

    For applications that use features deprecated in MySQL 8.0 that have been removed in a higher MySQL series, statements may fail when replicated from a MySQL 8.0 master to a higher-series slave, or may have different effects on master and slave. To avoid such problems, applications that use features deprecated in 8.0 should be revised to avoid them and use alternatives when possible.

    • The utf8mb3 character set is deprecated. Please use utf8mb4 instead.

    • Because caching_sha2_password is the default authentication plugin in MySQL 8.0 and provides a superset of the capabilities of the sha256_password authentication plugin, sha256_password is deprecated and will be removed in a future MySQL version. MySQL accounts that authenticate using sha256_password should be migrated to use caching_sha2_password instead.

    • The validate_password plugin has been reimplemented to use the server component infrastructure. The plugin form of validate_password is still available but is deprecated and will be removed in a future version of MySQL. MySQL installations that use the plugin should make the transition to using the component instead. See Section 6.4.3.3, “Transitioning to the Password Validation Component”.

    • The ENGINE clause for the ALTER TABLESPACE and DROP TABLESPACE statements is deprecated.

    • The PAD_CHAR_TO_FULL_LENGTH SQL mode is deprecated.

    • AUTO_INCREMENT support is deprecated for columns of type FLOAT and DOUBLE (and any synonyms). Consider removing the AUTO_INCREMENT attribute from such columns, or convert them to an integer type.

    • The UNSIGNED attribute is deprecated for columns of type FLOAT, DOUBLE, and DECIMAL (and any synonyms). Consider using a simple CHECK constraint instead for such columns.

    • FLOAT(M,D) and DOUBLE(M,D) syntax to specify the number of digits for columns of type FLOAT and DOUBLE (and any synonyms) is a nonstandard MySQL extension. This syntax is deprecated.

    • The ZEROFILL attribute is deprecated for numeric data types, as is the display width attribute for integer data types. Consider using an alternative means of producing the effect of these attributes. For example, applications could use the LPAD() function to zero-pad numbers up to the desired width, or they could store the formatted numbers in CHAR columns.

    • For string data types, the BINARY attribute is a nonstandard MySQL extension that is shorthand for specifying the binary (_bin) collation of the column character set (or of the table default character set if no column character set is specified). In MySQL 8.0, this nonstandard use of BINARY is ambiguous because the utf8mb4 character set has multiple _bin collations, so the BINARY attribute is deprecated and support for it will be removed in a future MySQL version. Applications should be adjusted to use an explicit _bin collation instead.

      The use of BINARY to specify a data type or character set remains unchanged.

    • The nonstandard C-style &&, ||, and ! operators that are synonyms for the standard SQL AND, OR, and NOT operators, respectively, are deprecated. Applications that use the nonstandard operators should be adjusted to use the standard operators.

      Note

      Use of || is deprecated unless the PIPES_AS_CONCAT SQL mode is enabled. In that case, || signifies the SQL-standard string concatenation operator).

    • The JSON_MERGE() function is deprecated. Use JSON_MERGE_PRESERVE() instead.

    • The SQL_CALC_FOUND_ROWS query modifier and accompanying FOUND_ROWS() function are deprecated. See the FOUND_ROWS() description for information about an alternative strategy.

    • Support for TABLESPACE = innodb_file_per_table and TABLESPACE = innodb_temporary clauses with CREATE TEMPORARY TABLE is deprecated as of MySQL 8.0.13.

    • For SELECT statements, use of an INTO clause after FROM but not at the end of the SELECT is deprecated as of MySQL 8.0.20. It is preferred to place the INTO at the end of the statement.

      For UNION statements, these two variants containing INTO are deprecated as of MySQL 8.0.20:

      • In the trailing query block of a query expression, use of INTO before FROM.

      • In a parenthesized trailing block of a query expression, use of INTO, regardless of its position relative to FROM.

      See Section 13.2.10.1, “SELECT ... INTO Statement”, and Section 13.2.10.3, “UNION Clause”.

    • The mysql_upgrade client is deprecated because its capabilities for upgrading the system tables in the mysql system schema and objects in other schemas have been moved into the MySQL server. See Section 2.11.3, “What the MySQL Upgrade Process Upgrades”.

    • The --no-dd-upgrade server option is deprecated. It is superseded by the --upgrade option, which provides finer control over data dictionary and server upgrade behavior.

    • The mysql_upgrade_info file, which is created data directory and used to store the MySQL version number, is deprecated and will be removed in a future MySQL version.

    • The relay_log_info_file system variable and --master-info-file option are deprecated. Previously, these were used to specify the name of the relay log info log and master info log when relay_log_info_repository=FILE and master_info_repository=FILE were set, but those settings have been deprecated. The use of files for the relay log info log and master info log has been superseded by crash-safe slave tables, which are the default in MySQL 8.0.

    • The max_length_for_sort_data system variable is now deprecated due to optimizer changes that make it obsolete and of no effect.

    • These legacy parameters for compression of connections to the server are deprecated: The --compress client command-line option; the MYSQL_OPT_COMPRESS option for the mysql_options() C API function; the slave_compressed_protocol system variable. For information about parameters to use instead, see Section 4.2.6, “Connection Compression Control”.

    • Use of the MYSQL_PWD environment variable to specify a MySQL password is deprecated.

    • Use of VALUES() to access new row values in INSERT ... ON DUPLICATE KEY UPDATE is deprecated as of MySQL 8.0.20. Use aliases for the new row and columns, instead.

    • Because specifying ON ERROR before ON EMPTY when invoking JSON_TABLE() is counter to the SQL standard, this syntax is now deprecated in MySQL. Beginning with MySQL 8.0.20, the server prints a warning whenever you attempt to do so. When specifying both of these clauses in a single JSON_TABLE() invocation, make sure that ON EMPTY is used first.

    Features Removed in MySQL 8.0

    The following items are obsolete and have been removed in MySQL 8.0. Where alternatives are shown, applications should be updated to use them.

    For MySQL 5.7 applications that use features removed in MySQL 8.0, statements may fail when replicated from a MySQL 5.7 master to a MySQL 8.0 slave, or may have different effects on master and slave. To avoid such problems, applications that use features removed in MySQL 8.0 should be revised to avoid them and use alternatives when possible.

    • The innodb_locks_unsafe_for_binlog system variable was removed. The READ COMMITTED isolation level provides similar functionality.

    • The information_schema_stats variable, introduced in MySQL 8.0.0, was removed and replaced by information_schema_stats_expiry in MySQL 8.0.3.

      information_schema_stats_expiry defines an expiration setting for cached INFORMATION_SCHEMA table statistics. For more information, see Section 8.2.3, “Optimizing INFORMATION_SCHEMA Queries”.

    • Code related to obsoleted InnoDB system tables was removed in MySQL 8.0.3. INFORMATION_SCHEMA views based on InnoDB system tables were replaced by internal system views on data dictionary tables. Affected InnoDB INFORMATION_SCHEMA views were renamed:

      Table 1.1 Renamed InnoDB Information Schema Views

      Old NameNew Name
      INNODB_SYS_COLUMNS INNODB_COLUMNS
      INNODB_SYS_DATAFILES INNODB_DATAFILES
      INNODB_SYS_FIELDS INNODB_FIELDS
      INNODB_SYS_FOREIGN INNODB_FOREIGN
      INNODB_SYS_FOREIGN_COLS INNODB_FOREIGN_COLS
      INNODB_SYS_INDEXES INNODB_INDEXES
      INNODB_SYS_TABLES INNODB_TABLES
      INNODB_SYS_TABLESPACES INNODB_TABLESPACES
      INNODB_SYS_TABLESTATS INNODB_TABLESTATS
      INNODB_SYS_VIRTUAL INNODB_VIRTUAL

      After upgrading to MySQL 8.0.3 or later, update any scripts that reference previous InnoDB INFORMATION_SCHEMA view names.

    • The following features related to account management are removed:

      • Using GRANT to create users. Instead, use CREATE USER. Following this practice makes the NO_AUTO_CREATE_USER SQL mode immaterial for GRANT statements, so it too is removed, and an error now is written to the server log when the presence of this value for the sql_mode option in the options file prevents mysqld from starting.

      • Using GRANT to modify account properties other than privilege assignments. This includes authentication, SSL, and resource-limit properties. Instead, establish such properties at account-creation time with CREATE USER or modify them afterward with ALTER USER.

      • IDENTIFIED BY PASSWORD 'auth_string' syntax for CREATE USER and GRANT. Instead, use IDENTIFIED WITH auth_plugin AS 'auth_string' for CREATE USER and ALTER USER, where the 'auth_string' value is in a format compatible with the named plugin.

        Additionally, because IDENTIFIED BY PASSWORD syntax was removed, the log_builtin_as_identified_by_password system variable is superfluous and was removed.

      • The PASSWORD() function. Additionally, PASSWORD() removal means that SET PASSWORD ... = PASSWORD('auth_string') syntax is no longer available.

      • The old_passwords system variable.

    • The query cache was removed. Removal includes these items:

      • The FLUSH QUERY CACHE and RESET QUERY CACHE statements.

      • These system variables: query_cache_limit, query_cache_min_res_unit, query_cache_size, query_cache_type, query_cache_wlock_invalidate.

      • These status variables: Qcache_free_blocks, Qcache_free_memory, Qcache_hits, Qcache_inserts, Qcache_lowmem_prunes, Qcache_not_cached, Qcache_queries_in_cache, Qcache_total_blocks.

      • These thread states: checking privileges on cached query, checking query cache for query, invalidating query cache entries, sending cached result to client, storing result in query cache, Waiting for query cache lock.

      • The SQL_CACHE SELECT modifier.

      These deprecated query cache items remain deprecated, but have no effect, and will be removed in a future MySQL release:

      • SQL_NO_CACHE SELECT modifier.

      • The ndb_cache_check_time system variable.

      The have_query_cache system variable remains deprecated, always has a value of NO, and will be removed in a future MySQL release.

    • The data dictionary provides information about database objects, so the server no longer checks directory names in the data directory to find databases. Consequently, the --ignore-db-dir option and ignore_db_dirs system variables are extraneous and are removed.

    • The tx_isolation and tx_read_only system variables have been removed. Use transaction_isolation and transaction_read_only instead.

    • The sync_frm system variable has been removed because .frm files have become obsolete.

    • The secure_auth system variable and --secure-auth client option have been removed. The MYSQL_SECURE_AUTH option for the mysql_options() C API function was removed.

    • The multi_range_count system variable is removed.

    • The log_warnings system variable and --log-warnings server option have been removed. Use the log_error_verbosity system variable instead.

    • The global scope for the sql_log_bin system variable was removed. sql_log_bin has session scope only, and applications that rely on accessing @@GLOBAL.sql_log_bin should be adjusted.

    • The metadata_locks_cache_size and metadata_locks_hash_instances system variables are removed.

    • The unused date_format, datetime_format, time_format, and max_tmp_tables system variables are removed.

    • These deprecated compatibility SQL modes are removed: DB2, MAXDB, MSSQL, MYSQL323, MYSQL40, ORACLE, POSTGRESQL, NO_FIELD_OPTIONS, NO_KEY_OPTIONS, NO_TABLE_OPTIONS. They can no longer be assigned to the sql_mode system variable or used as permitted values for the mysqldump --compatible option.

      Removal of MAXDB means that the TIMESTAMP data type for CREATE TABLE or ALTER TABLE is treated as TIMESTAMP, and is no longer treated as DATETIME.

    • The deprecated ASC or DESC qualifiers for GROUP BY clauses are removed. Queries that previously relied on GROUP BY sorting may produce results that differ from previous MySQL versions. To produce a given sort order, provide an ORDER BY clause.

    • The EXTENDED and PARTITIONS keywords for the EXPLAIN statement have been removed. These keywords are unnecessary because their effect is always enabled.

    • These encryption-related items are removed:

      • The ENCODE() and DECODE() functions.

      • The ENCRYPT() function.

      • The DES_ENCRYPT(), and DES_DECRYPT() functions, the --des-key-file option, the have_crypt system variable, the DES_KEY_FILE option for the FLUSH statement, and the HAVE_CRYPT CMake option.

      In place of the removed encryption functions: For ENCRYPT(), consider using SHA2() instead for one-way hashing. For the others, consider using AES_ENCRYPT() and AES_DECRYPT() instead.

    • In MySQL 5.7, several spatial functions available under multiple names were deprecated to move in the direction of making the spatial function namespace more consistent, the goal being that each spatial function name begin with ST_ if it performs an exact operation, or with MBR if it performs an operation based on minimum bounding rectangles. In MySQL 8.0, the deprecated functions are removed to leave only the corresponding ST_ and MBR functions:

      • These functions are removed in favor of the MBR names: Contains(), Disjoint(), Equals(), Intersects(), Overlaps(), Within().

      • These functions are removed in favor of the ST_ names: Area(), AsBinary(), AsText(), AsWKB(), AsWKT(), Buffer(), Centroid(), ConvexHull(), Crosses(), Dimension(), Distance(), EndPoint(), Envelope(), ExteriorRing(), GeomCollFromText(), GeomCollFromWKB(), GeomFromText(), GeomFromWKB(), GeometryCollectionFromText(), GeometryCollectionFromWKB(), GeometryFromText(), GeometryFromWKB(), GeometryN(), GeometryType(), InteriorRingN(), IsClosed(), IsEmpty(), IsSimple(), LineFromText(), LineFromWKB(), LineStringFromText(), LineStringFromWKB(), MLineFromText(), MLineFromWKB(), MPointFromText(), MPointFromWKB(), MPolyFromText(), MPolyFromWKB(), MultiLineStringFromText(), MultiLineStringFromWKB(), MultiPointFromText(), MultiPointFromWKB(), MultiPolygonFromText(), MultiPolygonFromWKB(), NumGeometries(), NumInteriorRings(), NumPoints(), PointFromText(), PointFromWKB(), PointN(), PolyFromText(), PolyFromWKB(), PolygonFromText(), PolygonFromWKB(), SRID(), StartPoint(), Touches(), X(), Y().

      • GLength() is removed in favor of ST_Length().

    • The functions described in Section 12.16.4, “Functions That Create Geometry Values from WKB Values” previously accepted either WKB strings or geometry arguments. Geometry arguments are no longer permitted and produce an error. See that section for guidelines for migrating queries away from using geometry arguments.

    • The parser no longer treats N as a synonym for NULL in SQL statements. Use NULL instead.

      This change does not affect text file import or export operations performed with LOAD DATA or SELECT ... INTO OUTFILE, for which NULL continues to be represented by N. See Section 13.2.7, “LOAD DATA Statement”.

    • PROCEDURE ANALYSE() syntax is removed.

    • The client-side --ssl and --ssl-verify-server-cert options have been removed. Use --ssl-mode=REQUIRED instead of --ssl=1 or --enable-ssl. Use --ssl-mode=DISABLED instead of --ssl=0, --skip-ssl, or --disable-ssl. Use --ssl-mode=VERIFY_IDENTITY instead of --ssl-verify-server-cert options. (The server-side --ssl option remains unchanged.)

      For the C API, MYSQL_OPT_SSL_ENFORCE and MYSQL_OPT_SSL_VERIFY_SERVER_CERT options for mysql_options() correspond to the client-side --ssl and --ssl-verify-server-cert options and are removed. Use MYSQL_OPT_SSL_MODE with an option value of SSL_MODE_REQUIRED or SSL_MODE_VERIFY_IDENTITY instead.

    • The --temp-pool server option was removed.

    • The ignore_builtin_innodb system variable is removed.

    • The server no longer performs conversion of pre-MySQL 5.1 database names containing special characters to 5.1 format with the addition of a #mysql50# prefix. Because these conversions are no longer performed, the --fix-db-names and --fix-table-names options for mysqlcheck, the UPGRADE DATA DIRECTORY NAME clause for the ALTER DATABASE statement, and the Com_alter_db_upgrade status variable are removed.

      Upgrades are supported only from one major version to another (for example, 5.0 to 5.1, or 5.1 to 5.5), so there should be little remaining need for conversion of older 5.0 database names to current versions of MySQL. As a workaround, upgrade a MySQL 5.0 installation to MySQL 5.1 before upgrading to a more recent release.

    • The mysql_install_db program has been removed from MySQL distributions. Data directory initialization should be performed by invoking mysqld with the --initialize or --initialize-insecure option instead. In addition, the --bootstrap option for mysqld that was used by mysql_install_db was removed, and the INSTALL_SCRIPTDIR CMake option that controlled the installation location for mysql_install_db was removed.

    • The generic partitioning handler was removed from the MySQL server. In order to support partitioning of a given table, the storage engine used for the table must now provide its own (“native”) partitioning handler. The --partition and --skip-partition options are removed from the MySQL Server, and partitioning-related entries are no longer shown in the output of SHOW PLUGINS or in the INFORMATION_SCHEMA.PLUGINS table.

      Two MySQL storage engines currently provide native partitioning support: InnoDB and NDB. Of these, only InnoDB is supported in MySQL 8.0. Any attempt to create partitioned tables in MySQL 8.0 using any other storage engine fails.

      Ramifications for upgrades.  The direct upgrade of a partitioned table using a storage engine other than InnoDB (such as MyISAM) from MySQL 5.7 (or earlier) to MySQL 8.0 is not supported. There are two options for handling such a table:

      At least one of the two operations just listed must be performed for each partitioned non-InnoDB table prior to upgrading the server to MySQL 8.0. Otherwise, such a table cannot be used following the upgrade.

      Due to the fact that table creation statements that would result in a partitioned table using a storage engine without partitioning support now fail with an error (ER_CHECK_NOT_IMPLEMENTED), you must make sure that any statements in a dump file (such as that written by mysqldump) from an older version of MySQL that you wish to import into a MySQL 8.0 server that create partitioned tables do not also specify a storage engine such as MyISAM that has no native partitioning handler. You can do this by performing either of the following:

      • Remove any references to partitioning from CREATE TABLE statements that use a value for the STORAGE ENGINE option other than InnoDB.

      • Specifying the storage engine as InnoDB, or allow InnoDB to be used as the table's storage engine by default.

      For more information, see Section 23.6.2, “Partitioning Limitations Relating to Storage Engines”.

    • System and status variable information is no longer maintained in the INFORMATION_SCHEMA. These tables are removed: GLOBAL_VARIABLES, SESSION_VARIABLES, GLOBAL_STATUS, SESSION_STATUS. Use the corresponding Performance Schema tables instead. See Section 26.12.13, “Performance Schema System Variable Tables”, and Section 26.12.14, “Performance Schema Status Variable Tables”. In addition, the show_compatibility_56 system variable was removed. It was used in the transition period during which system and status variable information in INFORMATION_SCHEMA tables was moved to Performance Schema tables, and is no longer needed. These status variables are removed: Slave_heartbeat_period, Slave_last_heartbeat, Slave_received_heartbeats, Slave_retried_transactions, Slave_running. The information they provided is available in Performance Schema tables; see Migrating to Performance Schema System and Status Variable Tables.

    • The Performance Schema setup_timers table was removed, as was the TICK row in the performance_timers table.

    • The libmysqld embedded server library is removed, along with:

      • The mysql_options() MYSQL_OPT_GUESS_CONNECTION, MYSQL_OPT_USE_EMBEDDED_CONNECTION, MYSQL_OPT_USE_REMOTE_CONNECTION, and MYSQL_SET_CLIENT_IP options

      • The mysql_config --libmysqld-libs, --embedded-libs, and --embedded options

      • The CMake WITH_EMBEDDED_SERVER, WITH_EMBEDDED_SHARED_LIBRARY, and INSTALL_SECURE_FILE_PRIV_EMBEDDEDDIR options

      • The (undocumented) mysql --server-arg option

      • The mysqltest --embedded-server, --server-arg, and --server-file options

      • The mysqltest_embedded and mysql_client_test_embedded test programs

    • The mysql_plugin utility was removed. Alternatives include loading plugins at server startup using the --plugin-load or --plugin-load-add option, or at runtime using the INSTALL PLUGIN statement.

    • The resolveip utility is removed. nslookup, host, or dig can be used instead.

    • The resolve_stack_dump utility is removed. Stack traces from official MySQL builds are always symbolized, so there is no need to use resolve_stack_dump.

    • The following server error codes are not used and have been removed. Applications that test specifically for any of these errors should be updated. 

      ER_BINLOG_READ_EVENT_CHECKSUM_FAILURE
ER_BINLOG_ROW_RBR_TO_SBR
ER_BINLOG_ROW_WRONG_TABLE_DEF
ER_CANT_ACTIVATE_LOG
ER_CANT_CHANGE_GTID_NEXT_IN_TRANSACTION
ER_CANT_CREATE_FEDERATED_TABLE
ER_CANT_CREATE_SROUTINE
ER_CANT_DELETE_FILE
ER_CANT_GET_WD
ER_CANT_SET_GTID_PURGED_WHEN_GTID_MODE_IS_OFF
ER_CANT_SET_WD
ER_CANT_WRITE_LOCK_LOG_TABLE
ER_CREATE_DB_WITH_READ_LOCK
ER_CYCLIC_REFERENCE
ER_DB_DROP_DELETE
ER_DELAYED_NOT_SUPPORTED
ER_DIFF_GROUPS_PROC
ER_DISK_FULL
ER_DROP_DB_WITH_READ_LOCK
ER_DROP_USER
ER_DUMP_NOT_IMPLEMENTED
ER_ERROR_DURING_CHECKPOINT
ER_ERROR_ON_CLOSE
ER_EVENTS_DB_ERROR
ER_EVENT_CANNOT_DELETE
ER_EVENT_CANT_ALTER
ER_EVENT_COMPILE_ERROR
ER_EVENT_DATA_TOO_LONG
ER_EVENT_DROP_FAILED
ER_EVENT_MODIFY_QUEUE_ERROR
ER_EVENT_NEITHER_M_EXPR_NOR_M_AT
ER_EVENT_OPEN_TABLE_FAILED
ER_EVENT_STORE_FAILED
ER_EXEC_STMT_WITH_OPEN_CURSOR
ER_FAILED_ROUTINE_BREAK_BINLOG
ER_FLUSH_MASTER_BINLOG_CLOSED
ER_FORM_NOT_FOUND
ER_FOUND_GTID_EVENT_WHEN_GTID_MODE_IS_OFF__UNUSED
ER_FRM_UNKNOWN_TYPE
ER_GOT_SIGNAL
ER_GRANT_PLUGIN_USER_EXISTS
ER_GTID_MODE_REQUIRES_BINLOG
ER_GTID_NEXT_IS_NOT_IN_GTID_NEXT_LIST
ER_HASHCHK
ER_INDEX_REBUILD
ER_INNODB_NO_FT_USES_PARSER
ER_LIST_OF_FIELDS_ONLY_IN_HASH_ERROR
ER_LOAD_DATA_INVALID_COLUMN_UNUSED
ER_LOGGING_PROHIBIT_CHANGING_OF
ER_MALFORMED_DEFINER
ER_MASTER_KEY_ROTATION_ERROR_BY_SE
ER_NDB_CANT_SWITCH_BINLOG_FORMAT
ER_NEVER_USED
ER_NISAMCHK
ER_NO_CONST_EXPR_IN_RANGE_OR_LIST_ERROR
ER_NO_FILE_MAPPING
ER_NO_GROUP_FOR_PROC
ER_NO_RAID_COMPILED
ER_NO_SUCH_KEY_VALUE
ER_NO_SUCH_PARTITION__UNUSED
ER_OBSOLETE_CANNOT_LOAD_FROM_TABLE
ER_OBSOLETE_COL_COUNT_DOESNT_MATCH_CORRUPTED
ER_ORDER_WITH_PROC
ER_PARTITION_SUBPARTITION_ERROR
ER_PARTITION_SUBPART_MIX_ERROR
ER_PART_STATE_ERROR
ER_PASSWD_LENGTH
ER_QUERY_ON_MASTER
ER_RBR_NOT_AVAILABLE
ER_SKIPPING_LOGGED_TRANSACTION
ER_SLAVE_CHANNEL_DELETE
ER_SLAVE_MULTIPLE_CHANNELS_HOST_PORT
ER_SLAVE_MUST_STOP
ER_SLAVE_WAS_NOT_RUNNING
ER_SLAVE_WAS_RUNNING
ER_SP_GOTO_IN_HNDLR
ER_SP_PROC_TABLE_CORRUPT
ER_SQL_MODE_NO_EFFECT
ER_SR_INVALID_CREATION_CTX
ER_TABLE_NEEDS_UPG_PART
ER_TOO_MUCH_AUTO_TIMESTAMP_COLS
ER_UNEXPECTED_EOF
ER_UNION_TABLES_IN_DIFFERENT_DIR
ER_UNSUPPORTED_BY_REPLICATION_THREAD
ER_UNUSED1
ER_UNUSED2
ER_UNUSED3
ER_UNUSED4
ER_UNUSED5
ER_UNUSED6
ER_VIEW_SELECT_DERIVED_UNUSED
ER_WRONG_MAGIC
ER_WSAS_FAILED

    • The deprecated INFORMATION_SCHEMA INNODB_LOCKS and INNODB_LOCK_WAITS tables are removed. Use the Performance Schema data_locks and data_lock_waits tables instead.

      Note

      In MySQL 5.7, the LOCK_TABLE column in the INNODB_LOCKS table and the locked_table column in the sys schema innodb_lock_waits and x$innodb_lock_waits views contain combined schema/table name values. In MySQL 8.0, the data_locks table and the sys schema views contain separate schema name and table name columns. See Section 27.4.3.9, “The innodb_lock_waits and x$innodb_lock_waits Views”.

    • InnoDB no longer supports compressed temporary tables. When innodb_strict_mode is enabled (the default), CREATE TEMPORARY TABLE returns an error if ROW_FORMAT=COMPRESSED or KEY_BLOCK_SIZE is specified. If innodb_strict_mode is disabled, warnings are issued and the temporary table is created using a non-compressed row format.

    • InnoDB no longer creates .isl files (InnoDB Symbolic Link files) when creating tablespace data files outside of the MySQL data directory. The innodb_directories option now supports locating tablespace files created outside of the data directory.

      With this change, moving a remote tablespace while the server is offline by manually modifying an .isl file is no longer supported. Moving remote tablespace files is now supported by the innodb_directories option. See Section 15.6.3.6, “Moving Tablespace Files While the Server is Offline”.

    • The following InnoDB file format variables were removed:

      • innodb_file_format

      • innodb_file_format_check

      • innodb_file_format_max

      • innodb_large_prefix

      File format variables were necessary for creating tables compatible with earlier versions of InnoDB in MySQL 5.1. Now that MySQL 5.1 has reached the end of its product lifecycle, these options are no longer required.

      The FILE_FORMAT column was removed from the INNODB_TABLES and INNODB_TABLESPACES Information Schema tables.

    • The innodb_support_xa system variable, which enables support for two-phase commit in XA transactions, was removed. InnoDB support for two-phase commit in XA transactions is always enabled.

    • Support for DTrace was removed.

    • The JSON_APPEND() function was removed. Use JSON_ARRAY_APPEND() instead.

    • Support for placing table partitions in shared InnoDB tablespaces was removed in MySQL 8.0.13. Shared tablespaces include the InnoDB system tablespace and general tablespaces. For information about identifying partitions in shared tablespaces and moving them to file-per-table tablespaces, see Section 2.11.5, “Preparing Your Installation for Upgrade”.

    • Support for setting user variables in statements other than SET was deprecated in MySQL 8.0.13. This functionality is subject to removal in MySQL 9.0.

    • The --ndb perror option was removed. Use the ndb_perror utility instead.

    • The innodb_undo_logs variable was removed. The innodb_rollback_segments variables performs the same function and should be used instead.

    • The Innodb_available_undo_logs status variable was removed. The number of available rollback segments per tablespace may be retrieved using SHOW VARIABLES LIKE 'innodb_rollback_segments';

    • As of MySQL 8.0.14, the previously deprecated innodb_undo_tablespaces variable is no longer configurable. For more information, see Section 15.6.3.4, “Undo Tablespaces”.

    • Support for the ALTER TABLE ... UPGRADE PARTITIONING statement has been removed.

    • As of MySQL 8.0.16, support for the internal_tmp_disk_storage_engine system variable has been removed; internal temporary tables on disk now always use the InnoDB storage engine. See Storage Engine for On-Disk Internal Temporary Tables,for more information.

    • The DISABLE_SHARED CMake option was unused and has been removed.

    1.5 Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 8.0

    This section lists server variables, status variables, and options that were added for the first time, have been deprecated, or have been removed in MySQL 8.0.

    Options and Variables Introduced in MySQL 8.0

    The following system variables, status variables, and options are new in MySQL 8.0, and have not been included in any previous release series.

    Options and Variables Deprecated in MySQL 8.0

    The following system variables, status variables, and options have been deprecated in MySQL 8.0.

    • Compression: Whether the client connection uses compression in the client/server protocol. Deprecated as of MySQL 8.0.18.

    • expire_logs_days: Purge binary logs after this many days. Deprecated as of MySQL 8.0.3.

    • innodb_undo_tablespaces: Number of tablespace files that rollback segments are divided between. Deprecated as of MySQL 8.0.4.

    • log_bin_use_v1_row_events: Whether server is using version 1 binary log row events. Deprecated as of MySQL 8.0.18.

    • log_syslog: Whether to write error log to syslog. Deprecated as of MySQL 8.0.2.

    • master-info-file: The location and name of the file that remembers the master and where the I/O replication thread is in the master's binary logs. Deprecated as of MySQL 8.0.18.

    • max_length_for_sort_data: Max number of bytes in sorted records. Deprecated as of MySQL 8.0.20.

    • no-dd-upgrade: Prevent automatic upgrade of data dictionary tables at startup. Deprecated as of MySQL 8.0.16.

    • relay_log_info_file: File in which the slave records information about the relay logs. Deprecated as of MySQL 8.0.18.

    • slave_compressed_protocol: Use compression of master/slave protocol. Deprecated as of MySQL 8.0.18.

    • slave_rows_search_algorithms: Determines search algorithms used for slave update batching. Any 2 or 3 from the list INDEX_SEARCH, TABLE_SCAN, HASH_SCAN. Deprecated as of MySQL 8.0.18.

    • symbolic-links: Permit symbolic links for MyISAM tables. Deprecated as of MySQL 8.0.2.

    Options and Variables Removed in MySQL 8.0

    The following system variables, status variables, and options have been removed in MySQL 8.0.

    • Com_alter_db_upgrade: Count of ALTER DATABASE ... UPGRADE DATA DIRECTORY NAME statements. Removed in MySQL 8.0.0.

    • Innodb_available_undo_logs: Display the total number of InnoDB rollback segments; different from innodb_rollback_segments, which displays the number of active rollback segments. Removed in MySQL 8.0.2.

    • Qcache_free_blocks: Number of free memory blocks in the query cache. Removed in MySQL 8.0.3.

    • Qcache_free_memory: The amount of free memory for the query cache. Removed in MySQL 8.0.3.

    • Qcache_hits: Number of query cache hits. Removed in MySQL 8.0.3.

    • Qcache_inserts: Number of query cache inserts. Removed in MySQL 8.0.3.

    • Qcache_lowmem_prunes: Number of queries that were deleted from the query cache due to lack of free memory in the cache. Removed in MySQL 8.0.3.

    • Qcache_not_cached: Number of noncached queries (not cacheable, or not cached due to the query_cache_type setting). Removed in MySQL 8.0.3.

    • Qcache_queries_in_cache: Number of queries registered in the query cache. Removed in MySQL 8.0.3.

    • Qcache_total_blocks: The total number of blocks in the query cache. Removed in MySQL 8.0.3.

    • Slave_heartbeat_period: The slave's replication heartbeat interval, in seconds. Removed in MySQL 8.0.1.

    • Slave_last_heartbeat: Shows when the latest heartbeat signal was received, in TIMESTAMP format. Removed in MySQL 8.0.1.

    • Slave_received_heartbeats: Number of heartbeats received by a replication slave since previous reset. Removed in MySQL 8.0.1.

    • Slave_retried_transactions: The total number of times since startup that the replication slave SQL thread has retried transactions. Removed in MySQL 8.0.1.

    • Slave_running: The state of this server as a replication slave (slave I/O thread status). Removed in MySQL 8.0.1.

    • bootstrap: Used by mysql installation scripts. Removed in MySQL 8.0.0.

    • date_format: The DATE format (unused). Removed in MySQL 8.0.3.

    • datetime_format: The DATETIME/TIMESTAMP format (unused). Removed in MySQL 8.0.3.

    • des-key-file: Load keys for des_encrypt() and des_encrypt from given file. Removed in MySQL 8.0.3.

    • group_replication_allow_local_disjoint_gtids_join: Allow the current server to join the group even if it has transactions not present in the group. Removed in MySQL 8.0.4.

    • have_crypt: Availability of the crypt() system call. Removed in MySQL 8.0.3.

    • ignore-db-dir: Treat directory as nondatabase directory. Removed in MySQL 8.0.0.

    • ignore_builtin_innodb: Ignore the built-in InnoDB. Removed in MySQL 8.0.3.

    • ignore_db_dirs: Directories treated as nondatabase directories. Removed in MySQL 8.0.0.

    • innodb_checksums: Enable InnoDB checksums validation. Removed in MySQL 8.0.0.

    • innodb_disable_resize_buffer_pool_debug: Disables resizing of the InnoDB buffer pool. Removed in MySQL 8.0.0.

    • innodb_file_format: The format for new InnoDB tables. Removed in MySQL 8.0.0.

    • innodb_file_format_check: Whether InnoDB performs file format compatibility checking. Removed in MySQL 8.0.0.

    • innodb_file_format_max: The file format tag in the shared tablespace. Removed in MySQL 8.0.0.

    • innodb_large_prefix: Enables longer keys for column prefix indexes. Removed in MySQL 8.0.0.

    • innodb_locks_unsafe_for_binlog: Force InnoDB not to use next-key locking. Instead use only row-level locking. Removed in MySQL 8.0.0.

    • innodb_scan_directories: Defines directories to scan for tablespace files during InnoDB recovery. Removed in MySQL 8.0.4.

    • innodb_stats_sample_pages: Number of index pages to sample for index distribution statistics. Removed in MySQL 8.0.0.

    • innodb_support_xa: Enable InnoDB support for the XA two-phase commit. Removed in MySQL 8.0.0.

    • innodb_undo_logs: Defines the number of undo logs (rollback segments) used by InnoDB; an alias for innodb_rollback_segments. Removed in MySQL 8.0.2.

    • internal_tmp_disk_storage_engine: Storage engine for internal temporary tables. Removed in MySQL 8.0.16.

    • log-warnings: Log some noncritical warnings to the log file. Removed in MySQL 8.0.3.

    • log_builtin_as_identified_by_password: Whether to log CREATE/ALTER USER, GRANT in backward-compatible fashion. Removed in MySQL 8.0.11.

    • log_error_filter_rules: Filter rules for error logging. Removed in MySQL 8.0.4.

    • log_syslog: Whether to write error log to syslog. Removed in MySQL 8.0.13.

    • log_syslog_facility: Facility for syslog messages. Removed in MySQL 8.0.13.

    • log_syslog_include_pid: Whether to include server PID in syslog messages. Removed in MySQL 8.0.13.

    • log_syslog_tag: Tag for server identifier in syslog messages. Removed in MySQL 8.0.13.

    • max_tmp_tables: Unused. Removed in MySQL 8.0.3.

    • metadata_locks_cache_size: Size of the metadata locks cache. Removed in MySQL 8.0.13.

    • metadata_locks_hash_instances: Number of metadata lock hashes. Removed in MySQL 8.0.13.

    • multi_range_count: The maximum number of ranges to send to a table handler at once during range selects. Removed in MySQL 8.0.3.

    • old_passwords: Selects password hashing method for PASSWORD(). Removed in MySQL 8.0.11.

    • partition: Enable (or disable) partitioning support. Removed in MySQL 8.0.0.

    • query_cache_limit: Do not cache results that are bigger than this. Removed in MySQL 8.0.3.

    • query_cache_min_res_unit: Minimal size of unit in which space for results is allocated (last unit will be trimmed after writing all result data). Removed in MySQL 8.0.3.

    • query_cache_size: The memory allocated to store results from old queries. Removed in MySQL 8.0.3.

    • query_cache_type: Query cache type. Removed in MySQL 8.0.3.

    • query_cache_wlock_invalidate: Invalidate queries in query cache on LOCK for write. Removed in MySQL 8.0.3.

    • secure_auth: Disallow authentication for accounts that have old (pre-4.1) passwords. Removed in MySQL 8.0.3.

    • show_compatibility_56: Compatibility for SHOW STATUS/VARIABLES. Removed in MySQL 8.0.1.

    • skip-partition: Do not enable user-defined partitioning. Removed in MySQL 8.0.0.

    • sync_frm: Sync .frm to disk on create. Enabled by default. Removed in MySQL 8.0.0.

    • temp-pool: Using this option will cause most temporary files created to use a small set of names, rather than a unique name for each new file. Removed in MySQL 8.0.1.

    • time_format: The TIME format (unused). Removed in MySQL 8.0.3.

    • tx_isolation: The default transaction isolation level. Removed in MySQL 8.0.3.

    • tx_read_only: Default transaction access mode. Removed in MySQL 8.0.3.
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  • 原文地址：https://www.cnblogs.com/jinzhenshui/p/12488729.html
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