I like to advise people to avoid self-JOINs whenever possible because I've always found them to be performance dogs across large row sets. Woof!
Not sure this is faster than the EXISTS or IN solutions proposed earlier, but it will almost certainly be swifter than a self JOIN.
DECLARE @T TABLE (ProductID VARCHAR(50))
INSERT INTO @T
SELECT '003223' UNION ALL SELECT '003225' UNION ALL SELECT '003227'
UNION ALL SELECT '003227A' UNION ALL SELECT '003236' UNION ALL SELECT '003236A'
UNION ALL SELECT '003241' UNION ALL SELECT '003273' UNION ALL SELECT '003273A'
SELECT ProductID
FROM (
SELECT ProductID, m=MAX(n) OVER (PARTITION BY LEFT(ProductID, 6))
FROM (
SELECT ProductID
,n=ROW_NUMBER() OVER (PARTITION BY LEFT(ProductID, 6) ORDER BY (SELECT NULL))
FROM @T) a) b
WHERE m > 1
Anyway, that is another alternative you can consider.
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
[url url=http://www.sqlservercentral.com/articles/St