与MysQL DATEDIFF函数不一致

Question

好的，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

该查询返回值9。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

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

Answer 1

试着这样做

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

您将看到的不是结果行的计数，而是实际的行列表。这可能会帮助你弄清楚这件事。