mysql> select sn,id,info from s100 group by id; +-----+------+------+ | sn | id | info | +-----+------+------+ | 227 | 1 | aa | | 228 | 2 | bb | +-----+------+------+ 2 rows in set (0.02 sec) mysql> select sn,count(id),info from s100 group by id; +-----+-----------+------+ | sn | count(id) | info | +-----+-----------+------+ | 227 | 32768 | aa | | 228 | 1 | bb | +-----+-----------+------+ 2 rows in set (0.02 sec) mysql> mysql> mysql> show index from s100; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | s100 | 0 | PRIMARY | 1 | sn | A | 33366 | NULL | NULL | | BTREE | | | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 1 row in set (0.00 sec) mysql> show variables like '%tx_isolation%'; +---------------+----------------+ | Variable_name | Value | +---------------+----------------+ | tx_isolation | READ-COMMITTED | +---------------+----------------+ 1 row in set (0.00 sec) mysql> show variables like '%commit%'; +--------------------------------+-------+ | Variable_name | Value | +--------------------------------+-------+ | autocommit | OFF | | binlog_order_commits | ON | | innodb_api_bk_commit_interval | 5 | | innodb_commit_concurrency | 0 | | innodb_flush_log_at_trx_commit | 1 | +--------------------------------+-------+ 5 rows in set (0.00 sec) Session 1: mysql> select * from s100 where id=2 for update; +-----+------+------+ | sn | id | info | +-----+------+------+ | 228 | 2 | bb | +-----+------+------+ 1 row in set (0.02 sec) Session 2: Database changed mysql> insert into s100(id,info) values(9999,'fcadfad'); Query OK, 1 row affected (0.00 sec) RC模式下,是行锁 不会上升到表级锁