从php查询调用MySql函数

Question

我试图从php调用MySql函数。当我在MySql中测试查询时，它工作正常，但是当我从php尝试它时，我没有得到任何结果。

我的职能：

DROP FUNCTION IF EXISTS AddWorkDays;
DELIMITER $$
CREATE FUNCTION AddWorkDays
(
WorkingDays INT,
StartDate DATETIME
)
RETURNS DATETIME

BEGIN
DECLARE Count INT;
DECLARE i INT;
DECLARE NewDate DATETIME;
SET Count = 0;
SET i = 0;

WHILE (i < WorkingDays) DO
    BEGIN
        SELECT Count + 1 INTO Count;
        SELECT i + 1 INTO i;
        WHILE DAYOFWEEK(DATE_ADD(StartDate,INTERVAL Count DAY)) IN (6,7) DO
            BEGIN
                SELECT Count + 1 INTO Count;
            END;
        END WHILE;
    END;
END WHILE;

SELECT DATE_ADD(StartDate,INTERVAL Count DAY) INTO NewDate;
RETURN NewDate;

END;
$$

DELIMITER ;

和我的php调用查询

$res = mysql_query($conn,"UPDATE `subscribes`  SET `end_date`=  AddWorkDays(1,`end_date`)  where `end_date` >= '2016-09-18'");