there is an ISDATE function in SQL as well;

here's an example base don your post:

/*

/*

Eid Variable Date? Converted?

---- --------- ----------- -----------------------

1 na 0 NULL

2 none 0 NULL

3 4/18/2013 1 2013-04-18 00:00:00.000

4 18/2013 0 NULL

5 2013 1 2013-01-01 00:00:00.000

6 9999999 0 NULL

*/

WITH MySampleData (Eid,Variable)

AS

(

SELECT '1','na' UNION ALL

SELECT '2','none' UNION ALL

SELECT '3','4/18/2013' UNION ALL

SELECT '4','18/2013' UNION ALL

SELECT '5','2013' UNION ALL

SELECT '6','9999999'

)

SELECT

MySampleData.*,

ISDATE(Variable) AS [Date?],

CASE

WHEN ISDATE(Variable) = 1

THEN CONVERT(datetime,Variable)

ELSE NULL

END As [Converted?]

FROM MySampleData