SQL Use alias in Where statement

Question

I wounder how I could use an alias in a where statement.

Example :

SELECT SUBSTRING(Column1, 1, 4) + SUBSTRING(Column1, 4, 3)  AS Col1
FROM MyTable
W         


        

Answer 1

Actually, using alias won't make your query any faster as SQL optimizer is not as dumb as you think, so I'd just repeat the SUBSTRING expression again.