与Select MySQL 5.6相乘

Question

我想在MySQL 5.6中创建函数。这个函数将由计数玩家乘以param。但我不知道怎么做。

我想是这样的，但它没有按预期工作。

DROP FUNCTION IF EXISTS do_it;

DELIMITER $$
 CREATE FUNCTION do_it (s INT) RETURNS INT DETERMINISTIC
    BEGIN
    DECLARE k INT;
    SELECT COUNT(id_player) as allPlayers FROM players;
    SET k= allPlayers * s;
    RETURN k;
    END$$
DELIMITER ;

SELECT do_it(2);

Answer 1

而是这样做

DECLARE k INT;
declare multiplyvar int;
SELECT COUNT(id_player) into multiplyvar FROM players;
SET k = multiplyvar  * s;
RETURN k;