MySQL: value based on conditions

Question

I have a MySQL query where I would like it to have a pseudo column returned which is based off of:

• If columnW does not equal 0, it should be 1 BUT
• If columnX does not equal 0, it should be 2 BUT
• If columnY does not equal 0, it should be 3 BUT
• If columnZ does not equal 0, it should be 4

Hopefully that makes sense. My SQL isn't good enough to wrap my head around this.

Answer 1

Try using a case expression:

SELECT CASE WHEN columnZ <> 0 THEN 4
            WHEN columnY <> 0 THEN 3
            WHEN columnX <> 0 THEN 2
            WHEN columnW <> 0 THEN 1
            ELSE 0
       END AS your_alias_name
FROM ...

Answer 2

You can use CASE ... WHEN to do this.

See

mysql> SELECT CASE 1 WHEN 1 THEN 'one'
    ->     WHEN 2 THEN 'two' ELSE 'more' END;
        -> 'one'
mysql> SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END;
        -> 'true'
mysql> SELECT CASE BINARY 'B'
    ->     WHEN 'a' THEN 1 WHEN 'b' THEN 2 END;
        -> NULL