Best method for varchar date validation in Sybase (T-SQL)? - tsql

Question

I have a stored procedure which takes as its parameter a varchar which needs to be cast as a datetime for later use:
SET #the_date = CAST(#date_string AS DATETIME)
I'm expecting the date string to be supplied in the format "DD-MON-YYYY", but in an effort to code defensively, if for some reason it can't be cast successfully, I want to default to the system date and continue. In PL/SQL I could use exception handling to achieve this and I could do this fairly easily with regular expressions too, but the limited pattern matching supported out of the box by Sybase doesn't let me do this and I can't rely on third party libraries or extensions. Is there a simple way of doing this in T-SQL?
NB: using Sybase ASE 12.5.3, there is no ISDATE function

Answer 1

I'm having a similar issue. You might be able to do something like this:
SET arithabort arith_overflow off
SET #the_date = CAST(#date_string AS DATETIME)
IF #the_date is NULL
set #the_date = getdate()
SET arithabort arith_overflow on
However, this doesn't work well in a select. It will work well in a cursor (boo) or in logic before / after a SQL batch.

Answer 2

My goodness, if the question was about Microsoft SQL Server then we'd have been in business!
Sybase, sadly, is a whole 'nother database these days, since about 1997, in fact, give or take a year.
If the input format simply has to be 'DD-MON-YYYY' and no exceptions, then I think a fair amount of validation was be achieved by slicing the input using SUBSTR(), after first doing some simple things, such as checking length.
I thought that recent releases of Sybase (SQL Anywhere 11, for example) have regular expression support, however, although it's been a while since I've had to suffer T-SQL. Some googling leaves me in rather more doubt.

Answer 3

Can't you do something like this:
SELECT #the_date = CASE #date_string
WHEN '[0-9][0-9]-[A-Z][A-Z][A-Z]-[0-9][0-9][0-9][0-9]'
THEN CONVERT(datetime, #date_string)
ELSE GETDATE()
END
?

Answer 4

Found this in the second result in Google when searching for "validate date string sql".
----Invalid date
SELECT ISDATE('30/2/2007')
RETURNS : 0 (Zero)
----Valid date
SELECT ISDATE('12/12/20007')
RETURNS : 1 (ONE)
----Invalid DataType
SELECT ISDATE('SQL')
RETURNS : 0 (Zero)

Answer 5

Make sure SQL Server knows the order of Days, Months and Years in your string by executing
SET DATEFORMAT mdy;

Answer 6

Did you try convert instead of cast?
select convert( datetime , #date_string )