CASE value
WHEN [compare_value] THEN result
[WHEN [compare_value] THEN result ...]
[ELSE result] END
Return the result where value=compare_value.
If there was no matching result value, the result after ELSE is returned, or NULL if there is no ELSE part.
mysql>
mysql> SELECT CASE 1
-> WHEN 1 THEN 'one'
-> WHEN 2 THEN 'two'
-> ELSE 'more'
-> END;
+------------------------------------------------------------------------------------------------+
| CASE 1
WHEN 1 THEN 'one'
WHEN 2 THEN 'two'
ELSE 'more' END |
+------------------------------------------------------------------------------------------------+
| one |
+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)