此mySql脚本中的语法错误是什么

Question

我已经写了一个存储函数：

  USE sakila;

DROP FUNCTION IF EXISTS sumOfFilm;

DELIMITER $$

CREATE FUNCTION sumOfFilm(
    mStore_id TINYINT, mMonth VARCHAR(4), mYear VARCHAR(4))
BEGIN
    DECLARE @sumOfFilm INT;
    SELECT COUNT(*) INTO @sumOfFilm FROM rental
    INNER JOIN inventory ON rental.inventory_id=inventory.inventory_id
    INNER JOIN store ON store.store_id=inventory.store_id
    WHERE mStore_id=store.store_id AND
            mMonth=month(rental_date) AND
            mYear=year(rental_date)
    GROUP BY store.store_id;
    RETURN @sumOfFilm;
END$$

DELIMITER ;

当我执行它时，我收到一条错误消息：

错误1064（42000）：您的SQL语法有错误； 查看与您的MySQL服务器版本相对应的手册以获取正确的语法，以在'BEGIN DECLARE @sumOfFilm INT附近使用； 在第3行中选择COUNT（*）INTO @sumOfFilm FROM Rental INN'

请帮我 ：）

Answer 1

  USE sakila;

DROP FUNCTION IF EXISTS sumOfFilm;

DELIMITER $$

CREATE FUNCTION sumOfFilm(
    mStore_id TINYINT, mMonth VARCHAR(4), mYear VARCHAR(4))
BEGIN
    SELECT @sumOfFilm := COUNT(*) FROM rental
    INNER JOIN inventory ON rental.inventory_id=inventory.inventory_id
    INNER JOIN store ON store.store_id=inventory.store_id
    WHERE mStore_id=store.store_id AND
            mMonth=month(rental_date) AND
            mYear=year(rental_date)
    GROUP BY store.store_id;
    RETURN INT @sumOfFilm;
END$$

DELIMITER ;

也可以尝试

SET @sumOfFilm = (SELECT COUNT(*) FROM rental)