Multiplying two columns which have been calculated on a CASE statement

Question

I am performing a SQL query in PostgreSQL using a CASE statement like this:

SELECT
    CASE column1
        WHEN something THEN 10
        ELSE 20
          


        

Answer 1

A CTE is a valid approach, giving additional options.
For a simple case like this a plain subquery is simpler and slightly faster.

SELECT *, (newcol2 * newcol3) AS newcol4
FROM  (
   SELECT CASE column1
            WHEN something THEN 10
            ELSE 20
            END AS newcol1
         ,CASE column12
            WHEN something THEN 30
            ELSE 40
            END AS newcol2
        ,COUNT(column3) AS newcol3
   FROM  table
   GROUP BY 1, 2
   ) AS sub

BTW: I removed newcol3 from GROUP BY, since you are running the aggregate function count() on it, which is slightly nonsensical.