-- Syntax
CASE
WHEN booleanExp THEN generalExp
...
ELSE generalExp
END

-- Traffic light classification
SELECT
  CASE
  WHEN mr > 150 THEN { 255c,   0c,   0c }
  WHEN mr > 100 THEN {   0c, 255c,   0c }
  ELSE               {   0c,   0c, 255c }
  END
FROM mr