How to use alias column name in where clause in SQL Server

Question

When I tried to perform the below code in SQL Server 2005 I am getting the error

Invalid column name DistanceFromAddress

Code:<

Answer 1

The WHERE clause is processed before the SELECT clause(*), and so the aliases aren't available. Move to using a subquery or CTE - here's a CTE:

; with Distances as (
    select SQRT(POWER(cast(Program_Latitude as float) - cast('41.5126237' as float), 2) +   
 POWER(cast(Program_Longitude as float) - cast('-81.6516411' as float), 2)) * 62.1371192 
 AS DistanceFromAddress
    from tblProgram
)
select * from Distances where DistanceFromAddress < 2

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(*) - well, systems are free to re-order operations as they see fit, so long as the result is "as if" the SQL statement was processed in a certain logical order. Of course, where this all goes wrong with SQL Server is where it produces errors because of conversion issues in the SELECT clause for rows/values that should be eliminated by the WHERE clause.