Syntax
CASE value WHEN compare-value THEN result [WHEN [compare-value] THEN result ...] [ELSE result] END
CASE WHEN condition THEN result [WHEN [condition] THEN result ...] [ELSE result] END
Purpose
In the returned result of the first syntax, value= compare-value. The prerequisite of the returned result of the second syntax is that the first condition is true. If no matching result exists, the returned result is the result after the ELSE operation. If no ELSE operation is involved, the return value is NULL.
Examples
obclient> SELECT CASE 'B' WHEN 'A' THEN 1 WHEN 'B' THEN 2 END;
+----------------------------------------------+
| CASE 'B' WHEN 'A' THEN 1 WHEN 'B' THEN 2 END |
+----------------------------------------------+
| 2 |
+----------------------------------------------+
1 row in set
obclient> SELECT CASE CONCAT('A','B') WHEN CONCAT('AB','') THEN 'A' WHEN 'B' THEN 'B' END;
+--------------------------------------------------------------------------+
| CASE CONCAT('A','B') WHEN CONCAT('AB','') THEN 'A' WHEN 'B' THEN 'B' END |
+--------------------------------------------------------------------------+
| A |
+--------------------------------------------------------------------------+
1 row in set
obclient> SELECT CASE WHEN 1>0 THEN 'TRUE' ELSE 'FALSE' END;
+--------------------------------------------+
| CASE WHEN 1>0 THEN 'TRUE' ELSE 'FALSE' END |
+--------------------------------------------+
| TRUE |
+--------------------------------------------+
1 row in set
