I have a datetime field in a large table where, obviously, almost every entry has a different value. We never search for a specific value except for maybe a DEXTRACT where I assume an index on the field would be useless unless we add a computed column for that value, right? But we often search where the field is not null or null. Do indexes help with a "is null"? And if they would, I assume I would decide whether to index based on how many are null; if 50% are null then an index probably wouldn't help but if only 5% are null then it might.
Karen
