Re: SQL performance - optimizer question

I'm coming into this discussion late, so I apologize if this is a stupid question, but I'm confused.

I'm confused with the clause

 	where	(key1 = :key1 or :key1 is null)
 	and	(key2 = :key2 or :key2 is null)
 	and	(key3 = :key3 or :key3 is null);

specifically with the 'or :key1 is null' piece. That 'or' condition does not include any reference to a database object, so I would think that it is either true for all rows or false for all rows, depending on the static value of :key1. I don't see how this would find null values of key1 when :key1 is null.  

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Bob Swisshelm                | swisshelm_at_Lilly.com     | 317 276 5472
Eli Lilly and Company        | Lilly Corporate Center  | Indianapolis, IN 46285