MySQL存储过程-向日期添加整数变量将返回null

Question

我正在编写我的第一个mysql过程。我有一个date变量和2个整数变量。我将两个整数变量相乘，然后将结果整数添加到date变量中。

例如：

pint=6;
noftimes=3
sdate=2020-05-05
totDays=pint*noftimes
edate=2020-05-05+totDays

我可以多个pint*noftimes，但不能添加sdate+totDays。而如果我添加sdate+10，则将获得正确的增量日期值。以下是我的过程：

DELIMITER $$
CREATE DEFINER=`pattu`@`localhost` PROCEDURE `getFieldWorkDates`(IN `p_id` INT, OUT `totDays` INT, OUT `edate` DATE)
BEGIN
DECLARE noftimes int;
DECLARE pint int;
DECLARE sdate DATE;
DECLARE tdays int;
SELECT startDate into sdate from projects where idprojects=p_id;
SELECT projectDuration into noftimes from projects where idprojects=p_id;
SELECT recFreq into pint from projects where idprojects=p_id;
SET totDays=pint*noftimes;
SET edate = sdate+(pint*noftimes);

END$$
DELIMITER ;

[执行此操作时，我收到消息，说明您的查询已成功执行。 0行受影响

Answer 1

SET edate = sdate+(pint*noftimes);

您不能将整数添加到日期。使用DATE_ADD（）函数。

---

CREATE 
DEFINER=pattu@localhost
PROCEDURE getFieldWorkDates ( IN p_id INT, 
                              OUT totDays INT, 
                              OUT edate DATE)
SELECT recFreq * projectDuration, 
       startDate + INTERVAL recFreq * projectDuration DAY 
INTO totDays, 
     edate 
FROM projects 
WHERE idprojects=p_id;