为什么将日期从nvarchar（max）转换为日期会引发错误？

Question

I have a date in this format

21-02-2018 

and using nvarchar(MAX)

I am trying to convert to date using

  select (Convert(Date, , 106)) from Certificates

  select (Convert(Date, IssueDate))

but it fails to convert.

Answer 1

Use try_convert() . However, I think you want format 105 (dd-mm-yyyy), not 106 (dd mon yyyy):

select try_convert(date, issuedate, 105)

This will return NULL instead of failing, when the format does not match. You can find these values:

select issuedate
from certificates
where try_convert(date, issuedate, 105) is null and
      issuedate is not null;

Answer 2

This is usually down to the format that the server is expecting the date to come in. I believe that it defaults to Month-Day-Year (American) rather than Day-Month-Year (British)

Try putting SET DATEFORMAT DMY at the start of your code to hint that the first part of the string is Day not month.