MySQL Tutorial/Miscellaneous Functions/RELEASE LOCK
RELEASE_LOCK(str): Releases the lock named by the string str that was obtained with GET_LOCK().
Returns 1 if the lock was released, 0 if the lock was not established by this thread (in which case the lock is not released), and NULL if the named lock did not exist.
22. 8. RELEASE_LOCK 22. 8. 1. RELEASE_LOCK(str): Releases the lock named by the string str that was obtained with GET_LOCK().