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yoyosh
Starting Member

27 Posts
Posted - 01/29/2013 :  02:12:32  Show Profile  Reply with Quote
I created simple query with several joins and a top(5) clause, which took more than a minute to execute.

However when I changed:

select top(5)

to

declare @i int
set @i = 5
select top (@i) ...

It took less than a second to execute. Why is that?

Below are links to execution plans:
top(5): http://imageshack.us/f/24/topsim.png/
top(@i): http://imageshack.us/f/203/topvar.png/

Thank you for help in advance

DonAtWork
Flowing Fount of Yak Knowledge

2111 Posts
Posted - 01/29/2013 :  07:12:53  Show Profile  Reply with Quote
Perhaps the execution plan was cached after the first run, and will make any following run a lot faster? Try running it the first way again and see.








How to ask: http://weblogs.sqlteam.com/brettk/archive/2005/05/25/5276.aspx
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yoyosh
Starting Member

27 Posts
Posted - 01/29/2013 :  08:06:36  Show Profile  Reply with Quote
I tried. It does not affect execution times in both cases.
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James K
Flowing Fount of Yak Knowledge

1515 Posts
Posted - 01/29/2013 :  08:11:18  Show Profile  Reply with Quote
Enable execution plan (control-m) and run both in the same query window. It will show you the relative costs and query plans. Examine the different query plans to see what is different. Is it just the query that you have shown that you are running, or is there more to it? Is it part of a stored procedure? If it is part of a stored procedure (or even if it is not), you can try statement level recompilation hint (add OPTION (RECOMPILE) at the end of the statement) to see if that makes any difference.
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yoyosh
Starting Member

27 Posts
Posted - 01/29/2013 :  08:14:44  Show Profile  Reply with Quote
As you could see from my initial post, i enabled them from the beginning. I have even attached links to them. What can you say about them?
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James K
Flowing Fount of Yak Knowledge

1515 Posts
Posted - 01/29/2013 :  08:25:41  Show Profile  Reply with Quote
Ah, I didn't see that - I am not able to access images from behind the corporate firewall. Hopefully someone else who is able to see the images can comment.
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yoyosh
Starting Member

27 Posts
Posted - 01/30/2013 :  07:37:56  Show Profile  Reply with Quote
Anyone could help me on that?
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