从字符串转换为日期时间的转换失败

Question

我尝试了下面的示例函数...并且我尝试了许多其他方式，但我仍然收到错误，因为“从字符串转换日期时间时转换失败”.. 我所尝试的只是来自这个函数，我正在返回一个日期时间，但这里的某个地方它仍然是字符串...

请指教

declare  @V_Year nvarchar (4), @Test datetime , @t1 as datetime  , @t2 as datetime 
declare @Mon varchar(5) , @dayz varchar (5) , @GMTStart varchar(20)
set @Mon = '03' 
set @t1  = cast ( @Mon as datetime)
set @dayz = '01'
set @t2  = cast ( @dayz as datetime)
SELECT @V_Year =  DATEPART(year, getdate())
set @GMTStart  = @Mon + '-' + @dayz + '-' + convert(nvarchar,@V_Year)
set @Test = Cast(@GMTStart as datetime)
select @Test

Answer 1

您的代码正在创建当年 3 月 3 日的日期时间值。

日期字符串的解释取决于set dateformat，除非您使用格式yyyymmdd。

从你的代码中删除所有似乎没有任何用处的东西会让你得到这个。

select cast(cast(year(getdate()) as char(4))+'0301' as datetime)

Answer 2

我稍微修改了你的代码：

declare  
    @V_Year nvarchar (4), 
    @Test datetime , 
    @t1 as datetime , 
    @t2 as datetime 
declare 
    @Mon varchar(8), --here need to be varchar(8) because datetime has 8 digits
    @dayz varchar(5), 
    @GMTStart varchar(20)
set @Mon = '20130101' --here you must provide full date, not a part, because is not possible to convert just part of date into full date
set @t1  = cast (@Mon as datetime) --this will work with 
--set @dayz = '01'
--set @t2  = cast (@dayz as datetime) --this line not work with just day, must provide full date

SET @V_Year =  DATEPART(year, getdate()) --here first set a variable, and then select
SELECT @V_Year
set @GMTStart  = @Mon + '-' + @dayz + '-' + convert(nvarchar, @V_Year)
set @Test = Cast(@GMTStart as datetime)
select @Test