Best equivalent for IsInteger in SQL Server

If SQL Server 2005+, I'd enable CLR and create the function to support regexes. For SQL Server 2000, see this article for creating a UDF to do the same thing.

Then I'd use the regex: ^\d{5}$

1 approach is

zipcode NOT LIKE '%[^0-9]%'

Double negatives, got to love 'em!

Late entry that handles negative

ISNUMERIC(zipcode + '.0e0') --integer
ISNUMERIC(zipcode + 'e0')  --decimal

For more see this