The SELECT FOR UPDATE clause is used to lock rows in a table when an update or delete transaction is performed on the active set. It selects the rows of the table that have to be modified and locks each row in the result set.
This prevents any other user from accessing the same set of records while modification is being executed on the table. You should add the NOWAIT clause to the SELECT FOR UPDATE statement to prevent the procedure from waiting indefinitely in case the lock cannot be acquired. If the NOWAIT clause is used, the control will return to the program in case the requested rows have been locked by another user.
