Question

I am using SQL Server 2008 R2

I just want to test if something exists in a table

IF EXISTS (SELECT * FROM ta WHERE ca = 'abc') PRINT 'YES'
IF EXISTS (SELECT ca FROM ta WHERE ca = 'abc') PRINT 'YES'
IF EXISTS (SELECT 1 FROM ta WHERE ca = 'abc') PRINT 'YES'
IF EXISTS (SELECT (1) FROM ta WHERE ca = 'abc') PRINT 'YES'
IF EXISTS (SELECT TOP 1 1 FROM ta WHERE ca = 'abc') PRINT 'YES'

Do they have any differences in result/side effect/performance (no matter how tiny)?

Thank you

Answer 1

Absolutely no difference – the IF EXISTS(...) will only check for existence of rows based on the WHERE clause in your statement.

Everything else in the statement is irrelevant – doesn’t make any difference whether you use SELECT * or SELECT 1 or or SELECT TOP 1 *. Even using SELECT * .... does NOT select all columns from the table – it again just checks for existence of the data based on the WHERE clause.

All five queries have exactly the same execution plan