Create Sybase function with exception handling

Question

I want to create function to use it in creation of view. In my table there are strings (strings are consists only of 8 digits) that I'm converting into DATE.

My function is:

CREATE FUNCTION MY.FUNCTION(@date int)
  RETURNS DATE 
AS
BEGIN
  RETURN CONVERT(DATETIME, @date)
END

If I use smth like SELECT FUNCTION('20170323') FROM TABLE it works as expected. But if I'll try smth like SELECT FUNCTION('77777777') FROM TABLE it fails of course... But if it fail I need to retut NULL! After some digging I have no result about function modification. How to add exception handling in my function properly to return date on NULL if it fails?

Answer 1

After a long investigation and lot of efforts I've found my solution:

CREATE FUNCTION MY_FUNCTION(@date CHAR(20))
  RETURNS DATE
AS
BEGIN
RETURN
(CASE
  WHEN ISDATE(@date) = 0
  THEN NULL
  ELSE CAST(@date AS DATE)
END)
END

Sybase method ISDATE() doing all magic in this case without throwing exception...