13.6.5.1 CASE Syntax

The CASE statement for stored programs implements a complex conditional construct.

Note

There is also a CASE expression, which differs from the CASE statement described here. See Section 12.4, "Control Flow Functions". The CASE statement cannot have an ELSE NULL clause, and it is terminated with END CASE instead of END

For the first syntax, case_value is an expression. This value is compared to the when_value expression in each WHEN clause until one of them is equal. When an equal when_value is found, the corresponding THEN clause statement_list executes. If no when_value is equal, the ELSE clause statement_list executes, if there is one.

This syntax cannot be used to test for equality with NULL because NULL = NULL is false. see Section 3.3.4.6, "Working with NULL Values".

For the second syntax, each WHEN clause search_condition expression is evaluated until one is true, at which point its corresponding THEN clause statement_list executes. If no search_condition is equal, the ELSE clause statement_list executes, if there is one.

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 SQL statements; an empty statement_list is not permitted.

To handle situations where no value is matched by any WHEN clause, use and ELSE containing an empty BEGIN ... END block, as shown in this example.(The indentation used here is the ELSE clause is for purposes of clarity only, and is not otherwise significant.)

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;
$$