IF condition in Select Statement SQL Server

The CASE statement is the closest to IF Else in SQL and is supported on all versions of SQL Server

SELECT CAST(
             CASE 
                  WHEN Obsolete = 'N' or InStock = 'Y' 
                     THEN 1 
                  ELSE 0 
             END AS bit) as Salable, * 
FROM Product

You only need to do the CAST if you want the result as a boolean value, if you are happy with an int, this works:

SELECT CASE 
            WHEN Obsolete = 'N' or InStock = 'Y' 
               THEN 1 
               ELSE 0 
       END as Salable, * 
FROM Product
CASE statements can be embedded in other CASE statements and even included in aggregates.