SQL_DATA_TYPE and SQL_DATETIME_SUB is always NULL

This column is the same as the DATA_TYPE column, except for interval and datetime data types.
For interval and datetime data types, the SQL_DATA_TYPE field in the result set will return SQL_INTERVAL or SQL_DATETIME, and the SQL_DATETIME_SUB field will return the subcode for the specific interval or datetime data type. (See Appendix D: Data Types.)