j.heidrich (1/21/2014)
Many thanks for your anwers.I tried the two different approaches from dwain.c with my sample table with 100k nvarchar(50) strings. On my machine with Win 8 64, SQL Server 2012, Core i7 2.4 Ghz and 16 GB RAM the second version without LAG function took around 5 seconds. The first version with LAG executed for 12 minutes when I aborted it!! Slight difference...
With the other three approaches I have to admit that I can't get it to work with my sample table. How can I incorporate a column from my table into the code instead of the @code parameter?
Anyway, I think the 5 seconds will be hard to beat.
Thanks for posting those performance results. I was just having a bit of fun with LAG, knowing it wouldn't be as good as the option without it. I'm casting my net wide to find an instance where LAG beats an earlier code pattern in performance and your test shows me this ain't one of 'em.
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]
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