SQL Pocket Guide, 3rd Edition

CASE Expressions: Searched

Searched CASE expressions associate a list of alternative return values with a list of true/false conditions. They also allow you to implement an IS NULL test. For example:

SELECT u.name,
   CASE
      WHEN u.open_to_public = 'y' THEN 'Welcome!'
      WHEN u.open_to_public = 'n' THEN 'Go Away!'
      WHEN u.open_to_public IS NULL THEN 'Null!'
      ELSE 'Bad code!'
   END AS column_alias
FROM upfall u;

Null is returned when no condition is TRUE and no ELSE is specified. If multiple conditions are TRUE, the first-listed condition takes precedence.