13.6.5.2 If Syntax

The IF statement for stored programs implements a basic conditional construct.

Note

There is also an IF() function, which differs from the IF statement described here. See Section 12.4, "Control Flow Functions". The IF statement can have THEN, ELSE, and ELSEIF clauses, and it is terminated with END IF.

if the search_condition evaluates to true, the corresponding THEN or ELSEIF clause statement_list executes. If no search_condition matches, the ELSE clause statement_list executes.

Each statement_list consists of one or more SQL statements; an empty statement_list is not permitted.

An IF ... END IF block, like all other flow-control blocks used within stored programs, must be terminated with a semicolon, as shown in this example:

DELIMITER $$

CREATE FUNCTION SimpleCompare(n INT, m INT)
    RETURNS VARCHAR(20)
    BEGIN
        DECLARE s VARCHAR(20);

        IF n > m THEN SET s = '>';
        ELSEIF n = m THEN SET s = '=';
        ELSE SET s = '<';
        END IF;

        SET s = CONCAT(n, ' ', s, ' ', m);

        RETURN s;
    END
$$

As with other flow-control constructs, IF ... END IF blocks may be nested within other flow-control constructs, including other IF statements. Each IF must be terminated by its own END IF followed by a semicolon. You can use indentation to make nested flow-control blocks more easily readable by humans (although this is not required by MySQL), as show here:

DELIMITER $$

CREATE FUNCTION VerboseComapre(n INT, m INT)
    RETURNS VARCHAR(50)

    BEGIN
        DECLARE s VARCHAR(50);
        IF n = m THEN SET s = 'equals';
        ELSE
            IF n > m THEN SET s = 'greater';
            ELSE SET s = 'less';
            END IF;

            SET s = CONCAT('is ', s, 'than');
        END IF;

        SET s = CONCAT(n, ' ', s, ' ', m, '.');

        RETURN s;
    END
$$

In this example, the inner IF is evaluated only if n is not equal to m.