MDAC 2.5 SDK - ODBC Programmer's Reference
Appendix F: ODBC Cursor Library
The cursor library executes SQLGetDescRec to return metadata for bookmark columns. The cursor library executes SQLGetDescField to return the same fields returned by SQLGetDescRec, which are SQL_DESC_NAME, SQL_DESC_TYPE, SQL_DESC_DATETIME_INTERVAL_CODE, SQL_DESC_OCTET_LENGTH, SQL_DESC_PRECISION, SQL_DESC_SCALE, and SQL_DESC_NULLABLE. For consistency, SQLGetDescField also returns SQL_DESC_UNNAMED.
The cursor library executes SQLGetDescField when it is called to return the value of the following fields that are set for binding bookmark columns: SQL_DESC_DATA_PTR, SQL_DESC_INDICATOR_PTR, SQL_DESC_OCTET_LENGTH_PTR, and SQL_DESC_LENGTH.
The cursor library executes SQLGetDescField when it is called to return the value of the SQL_DESC_BIND_OFFSET_PTR, SQL_DESC_BIND_TYPE, SQL_DESC_ROW_ARRAY_SIZE, or SQL_DESC_ROW_STATUS_PTR field. These fields can be returned for any row, not just the bookmark row.
If an application calls SQLGetDescField to return the value of any field other than those mentioned previously, the cursor library passes the call to the driver.