# datediff

## Syntax

`DATETIME DATEDIFF(DATETIME expr1,DATETIME expr2)`

## Description

计算expr1 - expr2，结果精确到天。

expr1 和 expr2 参数是合法的日期或日期/时间表达式。

注释：只有值的日期部分参与计算。

## Examples

```
mysql> select datediff(CAST('2007-12-31 23:59:59' AS DATETIME), CAST('2007-12-30' AS DATETIME));
+-----------------------------------------------------------------------------------+
| datediff(CAST('2007-12-31 23:59:59' AS DATETIME), CAST('2007-12-30' AS DATETIME)) |
+-----------------------------------------------------------------------------------+
|                                                                                 1 |
+-----------------------------------------------------------------------------------+

mysql> select datediff(CAST('2010-11-30 23:59:59' AS DATETIME), CAST('2010-12-31' AS DATETIME));
+-----------------------------------------------------------------------------------+
| datediff(CAST('2010-11-30 23:59:59' AS DATETIME), CAST('2010-12-31' AS DATETIME)) |
+-----------------------------------------------------------------------------------+
|                                                                               -31 |
+-----------------------------------------------------------------------------------+
```