Syntax
------

CASE case_value
  WHEN when_value THEN statement_list
  [WHEN when_value THEN statement_list] ...
  [ELSE statement_list]
END CASE

Or:

CASE
  WHEN search_condition THEN statement_list
  [WHEN search_condition THEN statement_list] ...
  [ELSE statement_list]
END CASE

Description
-----------

The text on this page describes the CASE statement for stored programs. See
the CASE OPERATOR for details on the CASE operator outside of stored programs.

The CASE statement for stored programs implements a complex conditional
construct. If a search_condition evaluates to true, the corresponding SQL
statement list is executed. If no search condition matches, the statement list
in the ELSE clause is executed. Each statement_list consists of one or more
statements.

The CASE statement cannot have an ELSE NULL clause, and it is terminated with
END CASE instead of END. implements a complex conditional construct. If a
search_condition evaluates to true, the corresponding SQL statement list is
executed. If no search condition matches, the statement list in the ELSE
clause is executed. Each statement_list consists of one or more statements.

If no when_value or search_condition matches the value tested and the CASE
statement contains no ELSE clause, a Case not found for CASE statement error
results.

Each statement_list consists of one or more statements; an empty
statement_list is not allowed. To handle situations where no value is matched
by any WHEN clause, use an ELSE containing an empty BEGIN ... END block, as
shown in this example:

DELIMITER |
CREATE PROCEDURE p()
BEGIN
 DECLARE v INT DEFAULT 1;
 CASE v
  WHEN 2 THEN SELECT v;
  WHEN 3 THEN SELECT 0;
  ELSE BEGIN END;
 END CASE;
END;
|

The indentation used here in the ELSE clause is for purposes of clarity only,
and is not otherwise significant. See Delimiters in the mysql client for more
on the use of the delimiter command.

Note: The syntax of the CASE statement used inside stored programs differs
slightly from that of the SQL CASE expression described in CASE OPERATOR. The
CASE statement cannot have an ELSE NULL clause, and it is terminated with END
CASE instead of END.

URL: https://mariadb.com/kb/en/case-statement/