• SAVEPOINT


    from:
    http://www.postgresql.org/docs/8.4/interactive/sql-savepoint.html

    SAVEPOINT
    Name
    SAVEPOINT -- define a new savepoint within the current transaction
    Synopsis

    SAVEPOINT savepoint_name

    Description

    SAVEPOINT establishes a new savepoint within the current transaction.

    A savepoint is a special mark inside a transaction that allows all commands that are executed after it was established to be rolled back, restoring the transaction state to what it was at the time of the savepoint.
    Parameters

    savepoint_name

        The name to give to the new savepoint.

    Notes

    Use ROLLBACK TO SAVEPOINT to rollback to a savepoint. Use RELEASE SAVEPOINT to destroy a savepoint, keeping the effects of commands executed after it was established.

    Savepoints can only be established when inside a transaction block. There can be multiple savepoints defined within a transaction.
    Examples

    To establish a savepoint and later undo the effects of all commands executed after it was established:

    BEGIN;
        INSERT INTO table1 VALUES (1);
        SAVEPOINT my_savepoint;
        INSERT INTO table1 VALUES (2);
        ROLLBACK TO SAVEPOINT my_savepoint;
        INSERT INTO table1 VALUES (3);
    COMMIT;

    The above transaction will insert the values 1 and 3, but not 2.

    To establish and later destroy a savepoint:

    BEGIN;
        INSERT INTO table1 VALUES (3);
        SAVEPOINT my_savepoint;
        INSERT INTO table1 VALUES (4);
        RELEASE SAVEPOINT my_savepoint;
    COMMIT;

    The above transaction will insert both 3 and 4.
    Compatibility

    SQL requires a savepoint to be destroyed automatically when another savepoint with the same name is established. In PostgreSQL, the old savepoint is kept, though only the more recent one will be used when rolling back or releasing. (Releasing the newer savepoint will cause the older one to again become accessible to ROLLBACK TO SAVEPOINT and RELEASE SAVEPOINT.) Otherwise, SAVEPOINT is fully SQL conforming.
    See Also
    BEGIN, COMMIT, RELEASE SAVEPOINT, ROLLBACK, ROLLBACK TO SAVEPOINT
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  • 原文地址:https://www.cnblogs.com/luoyaoquan/p/2140592.html
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