Question

I want to do something like this

declare @a int=1
if (@a=1)
with cte as 
(
select UserEmail from UserTable 
)
else
with cte as
(
select UserID from UserTable
)
select * from cte

This is just the example, my actual query is far more complex. So I don’t want to write the SELECT statement inside IF and ELSE statement twice after the CTE.

Answer 1

If possible, find a way to avoid the if statement entirely.

E.g. in such a trivial example as in your question:

;with CTE as (
      select UserEmail from UserTable where @a = 1
      union all
      select UserID from UserTable where @a != 1 or @a is null
)
select /* single select statement here */

It should generally be possible to compose one or more distinct queries into a final UNION ALL cte, instead of using if – after all, both of the queries being combined must have compatible result sets anyway, for your original question to make sense.