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SQL Query Performance

Author

Topic

cosmo74
Starting Member

1 Post

Posted - 2005-09-06 : 10:42:08

Performance around EXISTS - is there any difference, in terms of overhead, between:

EXISTS (Select 1..)

and

EXISTS (Select *)
??

madhivanan
Premature Yak Congratulator

22864 Posts

Posted - 2005-09-06 : 10:44:37

I think there is no significant difference
Set the Execution Plan and test it

Madhivanan

Failing to plan is Planning to fail

nathans
Aged Yak Warrior

938 Posts

Posted - 2005-09-06 : 10:49:27

Probably nothing between * vs 1.
The performance you gain by using EXISTS:

[url]http://www.sqlteam.com/item.asp?ItemID=14820[/url]

Nathan Skerl

Kristen
Test

22859 Posts

Posted - 2005-09-06 : 11:27:37

Hi cosmo74, Welcome to SQL Team!

I believe that the more common convention is

EXISTS (Select *)

It supposedly allows SQL Server to choose which column, and therefore which index etc., it will use to give best performance. but I think in practice SELECT 1 will probably do the same thing.

Kristen

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