如果差值小于0，则MySQL选择0，否则选择差值

Question

我想获得StartDate和EndDate之间的区别，但如果差异小于0，我想要值0（EndDate可能在StartDate之前）。有没有办法在SELECT中执行此操作而不重复ROUND（）表达式？

SELECT StartDate, EndDate, 
IF(ROUND(TIMESTAMPDIFF(SECOND, StartDate, EndDate)/86400, 1) < 0, 0, ROUND(TIMESTAMPDIFF(SECOND, StartDate, EndDate)/86400, 1)) AS Duration
FROM table
WHERE StartDate <= '2016-06-02' AND EndDate >= '2016-06-01';

Answer 1

只需使用GREATEST()即可获得较大的0和差异。

SELECT StartDate, EndDate, 
GREATEST(ROUND(TIMESTAMPDIFF(SECOND, StartDate, EndDate)/86400, 1), 0) AS Duration
FROM table
WHERE StartDate <= '2016-06-02' AND EndDate >= '2016-06-01';