mysql - DATE_ADD 和 INTERVAL 函数中的语法错误

Question

鉴于此功能:

DROP FUNCTION IF EXISTS expiration_date;
DELIMITER $$
CREATE FUNCTION expiration_date(lic_class VARCHAR(2), born_on DATE, at DATE) RETURNS DATE
BEGIN
    DECLARE age INTEGER;
    DECLARE span INTEGER DEFAULT 0;
    SET age = YEAR(at) - YEAR(born_on);
    IF     age < 50                 THEN SET span = 10;
    ELSEIF age >= 50 AND age < 70   THEN SET span = 5;
    ELSEIF age >= 70 AND age < 80   THEN SET span = 3;
    ELSEIF age >= 80                THEN SET span = 2;
    END IF;

    DECLARE ret DATE;
    SET ret = DATE_ADD(at, INTERVAL span YEAR); 
    RETURN ret;
END $$
DELIMITER ;

它给了我:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE ret DATE; SET ret = DATE_ADD(at, INTERVAL span YEAR); RETURN' at line 12

这是为什么呢？我错过了什么？

Answer 1

根据to the DECLARE documentation

DECLARE is permitted only inside a BEGIN ... END compound statement and must be at its start, before any other statements.

因此，将DECLARE ret DATE;放在IF...ELSE block 之后是无效的。将其与其他 DECLARE 声明一起移至顶部。

DROP FUNCTION IF EXISTS expiration_date;
DELIMITER $$
CREATE FUNCTION expiration_date(lic_class VARCHAR(2), born_on DATE, at DATE) RETURNS DATE
BEGIN
    DECLARE age INTEGER;
    DECLARE span INTEGER DEFAULT 0;
    -- No reason not to DECLARE up here!
    DECLARE ret DATE;

    SET age = YEAR(at) - YEAR(born_on);
    IF     age < 50                 THEN SET span = 10;
    ELSEIF age >= 50 AND age < 70   THEN SET span = 5;
    ELSEIF age >= 70 AND age < 80   THEN SET span = 3;
    ELSEIF age >= 80                THEN SET span = 2;
    END IF;

    SET ret = DATE_ADD(at, INTERVAL span YEAR); 
    RETURN ret;
END $$
DELIMITER ;