Описание

ALTER LARGE OBJECT изменяет определение большого объекта.

Выполнить ALTER LARGE OBJECT может только владелец большого объекта. Чтобы сменить владельца, необходимо быть непосредственным или опосредованным членом новой роли-владельца. (Однако суперпользователь может изменять свойства больших объектов в любом случае.) В настоящее время единственное возможное изменение заключается в назначении нового владельца, так что всегда действуют оба ограничения.

Параметры

Совместимость

Оператор ALTER LARGE OBJECT отсутствует в стандарте SQL.

См. также

Description

Roll back all commands that were executed after the savepoint was established. The savepoint remains valid and can be rolled back to again later, if needed.

ROLLBACK TO SAVEPOINT implicitly destroys all savepoints that were established after the named savepoint.

Parameters

Notes

Use RELEASE SAVEPOINT to destroy a savepoint without discarding the effects of commands executed after it was established.

Specifying a savepoint name that has not been established is an error.

Cursors have somewhat non-transactional behavior with respect to savepoints. Any cursor that is opened inside a savepoint will be closed when the savepoint is rolled back. If a previously opened cursor is affected by a FETCH or MOVE command inside a savepoint that is later rolled back, the cursor remains at the position that FETCH left it pointing to (that is, the cursor motion caused by FETCH is not rolled back). Closing a cursor is not undone by rolling back, either. However, other side-effects caused by the cursor's query (such as side-effects of volatile functions called by the query) are rolled back if they occur during a savepoint that is later rolled back. A cursor whose execution causes a transaction to abort is put in a cannot-execute state, so while the transaction can be restored using ROLLBACK TO SAVEPOINT, the cursor can no longer be used.

Examples

To undo the effects of the commands executed after my_savepoint was established:

ROLLBACK TO SAVEPOINT my_savepoint;

Cursor positions are not affected by savepoint rollback:

BEGIN;

DECLARE foo CURSOR FOR SELECT 1 UNION SELECT 2;

SAVEPOINT foo;

FETCH 1 FROM foo;
 ?column? 
----------
        1

ROLLBACK TO SAVEPOINT foo;

FETCH 1 FROM foo;
 ?column? 
----------
        2

COMMIT;

Compatibility

The SQL standard specifies that the key word SAVEPOINT is mandatory, but Postgres Pro and Oracle allow it to be omitted. SQL allows only WORK, not TRANSACTION, as a noise word after ROLLBACK. Also, SQL has an optional clause AND [ NO ] CHAIN which is not currently supported by Postgres Pro. Otherwise, this command conforms to the SQL standard.

See Also