Why use Select 1

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Why use Select 1

Mike Aguilar

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Points: 137
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July 14, 2015 at 2:04 pm

#151426

IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'Index name here' AND object_id = OBJECT_ID('Table Name Here')
DROP INDEX ....
I was just wondering why some people use a 1 there instead of name or *?
Personal preference, best practices, ?
Thanks

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Luis Cazares SSC Guru Points: 183698 More actions · Answer 1

Mike Aguilar (7/14/2015)
IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'Index name here' AND object_id = OBJECT_ID('Table Name Here')
DROP INDEX ....
I was just wondering why some people use a 1 there instead of name or *?
Personal preference, best practices, ?
Thanks

I'll say that it's personal preference as it won't matter what is in the column list, as EXISTS only checks for rows. You could even use SELECT 1/0 and you won't get an error.

Luis C.
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Mike Aguilar SSC Enthusiast Points: 137 More actions · Answer 2

Thanks Luis.

You know I had to try that. You were right: no error.

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 3

Personally, to make it clear(er) that EXISTS doesn't care what the columns are.

And 1/0 works, but something like LOG(-1) doesn't. I suspect the latter is a parse-time error.

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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Jacob Wilkins One Orange Chip Points: 27976 More actions · Answer 4

GilaMonster (7/14/2015)
Personally, to make it clear(er) that EXISTS doesn't care what the columns are.
And 1/0 works, but something like LOG(-1) doesn't. I suspect the latter is a parse-time error.

Ah, now that's a very interesting new fact!

Something like this:

IF EXISTS (

select LOG(-1) from sys.objects)

SELECT 1

Interestingly, that seems version specific. It fails on my 2008 and 2008 R2 instances, but succeeds on all my 2012 and 2014 instances. I'll have to do some digging to see if I can find any sources for what may have changed.

Cheers!