日期时间到varchar转换错误

Question

I know tons of such questions are already here on SO, but my question is slightly different than questions that already exist.

Scenario: Database has ApptDt column of type DateTime, with values in format "yyyy-mm-dd hh:mm:ss". I am from India and dates are passed in European Format, "dd-mm-yyyy". So every time I am getting this error:

The Conversion of a Varchar Datatype to a datetime results in an out of range value

Sample Query 1:

  Declare @EffectiveDt as varchar(29)
  Set @EffectiveDt = '27/07/2013'
  print Convert(DateTime,@EffectiveDt,102) // throws above error 

Sample Query 2:

Declare @EffectiveDt as varchar(29)
Set @EffectiveDt = '07/27/2013'    
print Convert(DateTime,@EffectiveDt,104) // throws above error too

Question:

1. The two formats are valid and conversions are allowed in T-Sql; why are such errors thrown?

2. Are there any generic functions or scenarios to hold such to-and-from conversions inside SQL?

Answer 1

What you should be doing is NOT using regional formats like d/m/y or m/d/y in the first place. If you use an unambiguous string format like yyyymmdd then there will never be an issue and you don't have to find all kinds of crazy workarounds. Just format your dates in a clear and standard way in the first place.

Just because you're from India does not mean you have to use regional strings to represent dates. If you're letting people enter dates in free text (which is the only way I could explain you ended up with 07/27/2013, 27/07/2013 and 27-07-2013), stop doing that, or validate their input. If someone enters 05/06/2013, how are you going to know if they mean May 6th or June 5th? SQL Server can't tell either, and there is no magic way (like there is in Access) to force it to guess, and transpose the numbers if they aren't valid. That is actually pretty scary behavior.

Answer 2

Change 102 to 104 (german format)

SELECT Convert(DateTime,@EffectiveDt,104)  

Demo

Answer 3

只是CAST它而不是试图在一个非常特定的文化中CONVERT它：

SELECT CAST(@EffectiveDt AS DATETIME)