SQL Server's optimizer is smart enough to recognize that the predicate always evaluates to FALSE. So it doesn't have to do anything except form the metadata that makes up the result set.

Here's the show plan that is created:

StmtText                           
---------------------------------- 
select * from contact where 1=0

StmtText            
------------------- 
  |--Constant Scan

And to give you an idea, if we make a simple change so that we're using a variable instead of a constant, this is the showplan that gets generated:

StmtText                                 
---------------------------------------- 
declare @x int
set @x = 1

select * from contact where @x = 0


StmtText                                                                                                                   
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
  |--Filter(WHERE:(STARTUP EXPR([@x]=0)))
       |--Compute Scalar(DEFINE:([contact].[reversePhone_pager]=reverse([contact].[phone_pager]), [contact].[reversePhone_fax]=reverse([contact].[phone_fax]), [contact].[reversePhone_mobile]=reverse([contact].[phone_mobile]), [contact].[reversePhone_work]=reverse([contact].[phone_work]), [contact].[reversePhone_home]=reverse([contact].[phone_home])))
            |--Clustered Index Scan(OBJECT:([gs13].[dbo].[contact].[cidx_contact_groupid_contactid]))

Which is really interesting because it shows that SQL Server can optimize the predicate to either a TRUE nor FALSE until execution. So it has decided to scan the clustered index (basically doing a table scan) and evaluating the expression as part of the filter.

-Mike

>>

>>... WHERE 1=2
>>

>
>Interesting, that works. But, what exactly does that tell SQL Server in order to returns an empty cursor?