T-SQL: Check if date is in proper format within Where-Clause

Question

How is it possible to check within the where-clause, if the date parameter is set and if it's in the proper format ( dd/mm/yyyy ).

Here is my SP with parameter @birthdaysearch in format ( dd/mm/yyyy ):

Select *
From Clients as c
WHERE
    CASE ISDATE(@birthdaysearch)
        WHEN 0 THEN (c.BirthDay LIKE '%')
        WHEN 1 THEN (c.BirthDay LIKE CONVERT(datetime,@birthdaysearch,103))
    END

Why isn't that working?

Thanks for your help!

Answer 1

You have incorrect syntax:

Select *
From Clients as c
WHERE ISDATE(@birthdaysearch) = 0 OR 
      (ISDATE(@birthdaysearch) = 1 AND c.BirthDay LIKE CONVERT(datetime, @birthdaysearch, 103))

or:

Select *
From Clients as c
WHERE c.BirthDay LIKE CASE WHEN ISDATE(@birthdaysearch) = 0 THEN '%'                   
                           ELSE CONVERT(datetime, @birthdaysearch, 103) END

But it is very strange why are you comparing dates with LIKE ? I suggest you the following:

Select *
From Clients as c
WHERE c.BirthDay = CASE ISDATE(@birthdaysearch) WHEN 0 THEN c.BirthDay
                    ELSE CAST(@birthdaysearch AS DATE) END

Answer 2

Given the conversation in the comments, I think the following would be appropriate:

Select *
From Clients as c
WHERE COALESCE(@BirthDaySearch, c.BirthDay) = c.BirthDay

So, given that your parameter is a datetime type, and is nullable, there is no need to check the date format, as it will always be valid (or null) when it hits the sproc.