Question

I’m trying to do a request that looks like this

SELECT field1, field2, field3 = CASE
    WHEN field2 = 'something' THEN 'something'
    WHEN field1 IS NOT NULL and field2 IS NULL THEN 'somethingElse'
    ELSE NULL
    END
FROM SomeTable
WHERE field3 IS NOT NULL

This results in a syntax error. I have to rewrite the CASE in the WHERE instead of just refering to it. Is there a better way to achieve this ?

And out of curiosity, why is “WHERE field3 IS NOT NULL” refused while for example “ORDER BY field3” would pass ?

Answer 1

SELECT * 
FROM (
  SELECT field1, 
         field2, 
         CASE
            WHEN field2 = 'something' THEN 'something'
            WHEN field1 IS NOT NULL and field2 IS NULL THEN 'somethingElse'
           ELSE NULL
         END as field3
  FROM your_table
) T
WHERE field3 IS NOT NULL