October 21, 2012 at 5:39 pm
Hi all,
Very basic question. I was reading the MCTS 70-433 training kit book from Microsoft, and fairly early on, they make a claim which I don't really fully believe.
In it, they claim that the use of the NOT operator makes indexes unusable for the query optimiser. However, I'm sure that I've regularly used NOT and had no problem with the optimiser using indexes. IE:
SELECT ID
FROM Table
WHERE ID NOT IN (1, 2, 3, 4, 5)
I have a feeling that the statement was just a generalized claim, since the following query clearly would not use an index seek:
SELECT ID
FROM Table
WHERE NOT (ID = 5 AND Name = 'Andrew')
Since, because of the NOT operator and the way boolean logic works, that query translates into an OR (WHERE ID <> 5 OR Name <> 'Andrew').
So, is the claim in the book incorrect?
October 22, 2012 at 12:44 am
Yes, the claim in the book is incorrect and is a common myth.
p.s. Your second will be able to use indexes, but probably for a scan operation, not a seek (or for a ranged seek)
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
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