Best way to make query/update sequence atomic

I have a PL/SQL stored procedure which does a SELECT to test for the existence of a row satisfying a set of criteria, then either updates the existing row or inserts a new one. How do I ensure that two concurrent sessions don't both get 'no row found' and try to do the insert? Is there a standard technique for doing this? At present the only solution I can see is to use DBMS_LOCK to ensure that only one instance of the SP is executing at any time.

Apologies if this is an entry-level question - any suggestions appreciated.

Adrian Bowen Received on Fri Aug 27 1999 - 02:57:26 CDT