Question

I am using SQL server 2008 R2. I know I can use CONVERT with different format code as the third parameter to do the conversion to DATETIME first and CONVERT again to VARCHAR with another format code to change the display format.

The real problem now is I have mixed raw data in a single column. So my question is how do you write a single SELECT statement to display from mixed YYYY/MM/DD, DD/MM/YYYY all to DD/MM/YYYY?

I tried to use ISDATE() but it think 31/01/2013 is not a date while 01/01/2013 is a date. Now I could only think of to see if the YYYY is on the left or on the right to determine the correct input format, but I dont know how to write it out in a single SELECT statement.

Any procedure to change the format first then do a simple SELECT is not an option. I am not allowed to change the source.

Thank you

Answer 1

If you are sure that only those 2 formats (yyyy/mm/dd and dd/mm/yyyy) exist in the data, then you could probably get away with a CASE statement along the lines of:

CASE
  WHEN (SUBSTRING(dateColumn, 5, 1) = '/') THEN CONVERT(datetime, dateColumn, 111)
  ELSE CONVERT(datetime, dateColumn, 103)
END