Date conversion and culture: Difference between DATE and DATETIME

Question

I\'ve written a lot of answers about date or datetime conversions from strings. Living in a german speaking country, I\'m used to deal with non

Answer 1

(Started out as a comment, but...) To add some more data to marc_s's answer, datetime will also fail with yyyy-mm-dd HH:MM:ss - So

SET LANGUAGE GERMAN;
DECLARE @dateTimeFailes DATETIME ='2017-01-13 00:00:00';

Will result with the same error. However, Once you replace the space between the Date and Time parts with a T, SQL Server will suddenly understand the format -

SET LANGUAGE GERMAN;
DECLARE @dateTime DATETIME ='2017-01-13T00:00:00';

Will work as expected.

Here is a quick list of acceptable and unacceptable formats:

SET LANGUAGE GERMAN;
-- Correct 
DECLARE @date DATE ='2017-01-13';
DECLARE @dateTime DATETIME ='2017-01-13T00:00:00'; 
DECLARE @dateTimeDateOnly DATETIME ='20170113';

-- Incorrect
DECLARE @WrongFormatDateTime DATETIME ='2017-01-13 00:00:00'; 
DECLARE @WrongFormatDate DATETIME ='2017-01-13';

Answer 2

The ISO-8601 for DATETIME (the older type) is somehow "broken" or "adapted" (depending on whether you look at it as a bug or a feature) - you need to use YYYYMMDD (without any dashes) to make it work irrespective of the language settings.

For DATE or the DATETIME2(n) datatypes, this has been fixed and the "proper" ISO-8601 format YYYY-MM-DD will always be interpreted correctly.

-- OK because of "adapted" ISO-8601
SET LANGUAGE GERMAN;
DECLARE @dt DATETIME='20170113'; 

SELECT @dt;

SELECT CAST('20170113' AS DATETIME);
SELECT CONVERT(DATETIME, '20170113'); 

-- OK because of DATETIME2(n)
SET LANGUAGE GERMAN;
DECLARE @dt2 DATETIME2(0) = '2017-01-13'; 

SELECT @dt2;

SELECT CAST('2017-01-13' AS DATETIME2(0));
SELECT CONVERT(DATETIME2(0), '2017-01-13'); 

It's a quirk of the DATETIME type (and not the only one....) - just register it, know about it - and move on (meaning: don't use DATETIME anymore - use DATE or DATETIME2(n) instead - much nicer to work with!) :-)