rq,
Remember this:
1. DATETIME datatype ALWAYS is a date AND a time. If one or both are not provided MS SQL Server inserts the default.
2. You cannot use dates/times with DATE functions (DATEADD, DATEDIFF, etc) when they are VARCHAR, NVARCHAR, CHAR, NCHAR. To use DATE functions, the date and time MUST be DATETIME datatype. If you have them stored as VARCHAR, etc. you will need to convert/cast the data before using the DATE functions. Again, NULL cannot be converted/cast into DATETIME datatype.
-SQLBill