如何在sqlserver 2008中将nvarchar（50）转换为datetime

Question

您好我在SqlServer 2008中写了这个查询 但有些事情出了问题

select * from News_Table
where (DATEDIFF( DAY ,convert(datetime, NewsDate) , convert(datetime,@Todaydate )) <= @Count)

@NewsDate和@Todaydate是两个nvarchar参数，保存方式如下2014/11/16

运行此查询会给我一个错误：

Conversion failed when converting date and/or time from character string

Answer 1

尝试将正确的样式参数添加到转换函数中（请参阅MSDN：link）

即CONVERT(DATETIME, NewsDate, 111)（111是YYYY / MM / DD的样式）

然后你得到：

SELECT * 
FROM  News_Table
WHERE (DATEDIFF( DAY ,
                 CONVERT(DATETIME, NewsDate, 111) , 
                 CONVERT(DATETIME,@Todaydate, 111)
               ) <= @Count)

Answer 2

了解更多click here

SELECT convert(datetime, '2014/11/16', 111) as datetime

<强> OP

所以你的查询就像这样

Select * from News_Table
where (DATEDIFF( DAY ,convert(datetime, '2014/11/16', 111) , convert(datetime,@Todaydate,111 )) <= @Count)

Answer 3

使用Convert(datetime, @yourvalue, 111)

select * from News_Table
where (DATEDIFF( DAY ,convert(datetime, @NewsDate, 111) , convert(datetime,@Todaydate, 111 )) <= @Count)

http://www.sqlusa.com/bestpractices/datetimeconversion/

Answer 4

试试这个

SELECT * 
FROM News_Table
WHERE (DATEDIFF(DAY,CAST(NewsDate AS Datetime),CAST(@Todaydate AS Datetime)) <= @Count)

Answer 5

您需要执行类似的操作才能将该字符串转换为DATETIME数据类型

DECLARE @Date NVARCHAR(20) = '2013/11/16'

SELECT CAST((LEFT(@Date, 4) + SUBSTRING(@Date, 6 ,2) + RIGHT(@Date, 2)) AS DATETIME)

查询

select * from News_Table
where (DATEDIFF( DAY , CAST((LEFT(NewsDate, 4) + SUBSTRING(NewsDate, 6 ,2) + RIGHT(NewsDate, 2)) AS DATETIME)
                     , CAST((LEFT(@Todaydate, 4) + SUBSTRING(@Todaydate, 6 ,2) + RIGHT(@Todaydate, 2)) AS DATETIME)
                ) <= @Count)

注意

如果变量@Todaydate实际上存储了今天的日期，那么为什么不使用简单的GETDATE()函数。