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SQL As Understood By SQLite




syntax diagram savepoint-stmt


syntax diagram release-stmt


syntax diagram rollback-stmt

^SAVEPOINTs are a method of creating transactions, similar to BEGIN and COMMIT, except that the SAVEPOINT and RELEASE commands are named and may be nested.

^The SAVEPOINT command starts a new transaction with a name. ^The transaction names need not be unique. ^(A SAVEPOINT can be started either within or outside of a BEGIN...COMMIT.)^ ^(When a SAVEPOINT is the outer-most savepoint and it is not within a BEGIN...COMMIT then the behavior is the same as BEGIN DEFERRED TRANSACTION.)^

^The ROLLBACK TO command reverts the state of the database back to what it was just after the corresponding SAVEPOINT. ^Note that unlike that plain ROLLBACK command (without the TO keyword) the ROLLBACK TO command does not cancel the transaction. ^Instead of cancelling the transaction, the ROLLBACK TO command restarts the transaction again at the beginning. ^All intervening SAVEPOINTs are canceled, however.

^The RELEASE command is like a COMMIT for a SAVEPOINT. ^The RELEASE command causes all savepoints back to and including the most recent savepoint with a matching name to be removed from the transaction stack. ^The RELEASE of an inner transaction does not cause any changes to be written to the database file; it merely removes savepoints from the transaction stack such that it is no longer possible to ROLLBACK TO those savepoints. ^If a RELEASE command releases the outermost savepoint, so that the transaction stack becomes empty, then RELEASE is the same as COMMIT. ^The COMMIT command may be used to release all savepoints and commit the transaction even if the transaction was originally started by a SAVEPOINT command instead of a BEGIN command.

^If the savepoint-name in a RELEASE command does not match any savepoint currently in the transaction stack, then no savepoints are released, the database is unchanged, and the RELEASE command returns an error.

^Note that an inner transaction might commit (using the RELEASE command) but then later have its work undone by a ROLLBACK in an outer transaction. ^A power failure or program crash or OS crash will cause the outer-most transaction to rollback, undoing all changes that have occurred within that outer transaction, even changes that have supposedly been "committed" by the RELEASE command. ^Content is not actually committed on the disk until the outermost transaction commits.

There are several ways of thinking about the RELEASE command:

Transaction Nesting Rules

^The last transaction started will be the first transaction committed or rolled back.

^The BEGIN command only works if the transaction stack is empty, or in other words if there are no pending transactions. ^If the transaction stack is not empty when the BEGIN command is invoked, then the command fails with an error.

^The COMMIT command commits all outstanding transactions and leaves the transaction stack empty.

^The RELEASE command starts with the most recent addition to the transaction stack and releases savepoints backwards in time until it releases a savepoint with a matching savepoint-name. ^Prior savepoints, even savepoints with matching savepoint-names, are unchanged. ^If the RELEASE command causes the transaction stack to become empty (if the RELEASE command releases the outermost transaction from the stack) then the transaction commits.

^The ROLLBACK command without a TO clause rolls backs all transactions and leaves the transaction stack empty.

^The ROLLBACK command with a TO clause rolls back transactions going backwards in time back to the most recent SAVEPOINT with a matching name. ^The SAVEPOINT with the matching name remains on the transaction stack, but all database changes that occurred after that SAVEPOINT was created are rolled back. ^If the savepoint-name in a ROLLBACK TO command does not match any SAVEPOINT on the stack, then the ROLLBACK command fails with an error and leaves the state of the database unchanged.