create table T(ID int identity primary key) insert into T default values insert into T default values go select cast(ID as varchar(10)) as ID from T where ID = 1
The query above has a warning in the query plan.
<Warnings> <PlanAffectingConvert ConvertIssue="Cardinality Estimate" Expression="CONVERT(varchar(10),[xx].[dbo].[T].[ID],0)" /> </Warnings>
Why does it have the warning?
How could a cast in the field list affect the cardinality estimate?