There is one essential difference between the use of SELECT * and
SELECT 1. SELECT * will expand the column list and then throw what
isn’t needed out. Now, don’t take, “throw what isn’t needed out”
literally. The compilation of the query will simply determine which
columns are relevant and to be used. With SELECT 1, this step isn’t
performed during compilation..
It’s important to note that compilation is where the effects of this occur. The runtime versions of these different methods will be used functionally, the same with the same performance.
Generally we will not observe more difference between them.Using select 1 is best practice instead of select
e.g.
if exists (select * from test )
print 'test passed'
go
if exists (select 1 from test )
print 'test passed'
It’s important to note that compilation is where the effects of this occur. The runtime versions of these different methods will be used functionally, the same with the same performance.
Generally we will not observe more difference between them.Using select 1 is best practice instead of select
e.g.
if exists (select * from test )
print 'test passed'
go
if exists (select 1 from test )
print 'test passed'
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