case statement in SQL, how to return multiple variables?

Question

I would like to return multiple values in my case statement, such as :

SELECT
  CASE
    WHEN  THEN 
    WHEN          


        

Answer 1

Depending on your use case, instead of using a case statement, you can use the union of multiple select statements, one for each condition.

My goal when I found this question was to select multiple columns conditionally. I didn't necessarily need the case statement, so this is what I did.

For example:

  SELECT
    a1,
    a2,
    a3,
    ...
  WHERE 
    AND ()
  UNION
  SELECT
    b1,
    b2,
    b3,
    ...
  WHERE 
    AND ()
  UNION
  SELECT
  ...
-- and so on

Be sure that exactly one condition evaluates to true at a time.

I'm using Postgresql, and the query planner was smart enough to not run a select statement at all if the condition in the where clause evaluated to false (i.e. only one of the select statement actually runs), so this was also performant for me.