Lex, Thanks for this. I like it. Never thought of that before. Henry -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Lex de Haan Sent: Wednesday, December 07, 2005 3:31 AM To: oracle-l@xxxxxxxxxxxxx Subject: RE: Function based indexes? this just reminds me of an example I worked on a while ago with Diana Lorentz, for the SQL Reference, where two columns are involved: see http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14200/statements _501 0.htm#i2077034 and scroll down to this section: Using a Function-based Index to Define Conditional Uniqueness: Example ====================================================================== The following statement creates a unique function-based index on the oe.orders table that prevents a customer from taking advantage of promotion ID 2 ("blowout sale") more than once: CREATE UNIQUE INDEX promo_ix ON orders (CASE WHEN promotion_id = 2 THEN customer_id ELSE NULL END, CASE WHEN promotion_id = 2 THEN promotion_id ELSE NULL END); cheers, Lex. -- //www.freelists.org/webpage/oracle-l