不一致性与MySQL DATEDIFF功能

Question

好了，所以我有以下MySQL查询：

SELECT COUNT(*) FROM `dates` WHERE firstDate IS NOT NULL AND secondDate IS NOT NULL 
AND DATEDIFF(secondDate, firstDate) >= 30 

即查询返回9.值然后我使用以下查询：

SELECT COUNT(*) FROM `dates` WHERE firstDate IS NOT NULL AND secondDate IS NOT NULL 
AND DATEDIFF(secondDate, firstDate) >= 90 

第二个查询返回结果12.这怎么可能？这两个日期都是MySQL数据库中的日期数据类型。

Answer 1

尝试这样做

SELECT firstDate, secondDate, DATEDIFF(secondDate, firstDate) AS diff 
FROM `dates` WHERE firstDate IS NOT NULL AND secondDate IS NOT NULL 
AND DATEDIFF(secondDate, firstDate) >= 30 

SELECT firstDate, secondDate, DATEDIFF(secondDate, firstDate) AS diff 
FROM `dates` WHERE firstDate IS NOT NULL AND secondDate IS NOT NULL 
AND DATEDIFF(secondDate, firstDate) >= 90 

而是所产生的行数，你会看到实际的行名单。 这可能会帮助你弄清楚这一点。