By default, MySQL begins each client connection with autocommit mode enabled. When autocommit is enabled, MySQL does a commit after each SQL statement if that statement did not return an error. If an SQL statement returns an error, the commit or rollback behavior depends on the error. See Section 13.2.15, “InnoDB Error Handling”.

If you have the autocommit mode off and close a connection without explicitly committing the final transaction, MySQL rolls back that transaction.

For details about which statements implicitly end a transaction, as if you had done a COMMIT before executing the statement, see Section 12.4.3, “Statements That Cause an Implicit Commit”.