Historical version. PostgreSQL 7.4 has reached end of support. See the current manual.
ROLLBACK
Description
ROLLBACK rolls back the current transaction and causes all the updates made by the transaction to be discarded.
Notes
Use COMMIT to successfully terminate a transaction.
Issuing ROLLBACK when not inside a transaction does no harm, but it will provoke a warning message.
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Read the upstream documentation. For corrections, first check the current manual.