CODEWITHSUNDEEP
sql-server
karthik
karthik

Reputation: 341

SQL Server IF EXISTS

I have to insert data into table but only if it does not already exist.

I check for existing rows using:

IF EXISTS (SELECT 'X' FROM Table1 where id = @id)

Will the use of 'X' improve performance instead of using a column name?

Upvotes: 4

Views: 3162

Answers (3)

gbn
gbn

Reputation: 432230

No. You can use *,column name, NULL or even 1/0.

As per the ANSI standard, it should not be evaluated. Page 191 ANSI SQL 1992 Standard.

* is mentioned in MSDN

However, a better way is to use MERGE (SQL Server 2008) or simply catch the error. Previous SO answers from me: One, Two

Upvotes: 8

Ozten
Ozten

Reputation: 188

One technique would be to add a unique constraint on the column. Always insert a record and handle the failure case where that id already existed in the table.

Upvotes: 0

Andy White
Andy White

Reputation: 88355

It's probably negligible difference. I think the most common "pattern" I've seen is to just select 1 when you're just checking for existence, but I wouldn't worry about it too much.

select 1 from Table1...

Upvotes: 0

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