MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 11: Retrieving Results (Advanced)
SQLGetData operates on a single column of a single row and cannot fetch an array containing data from multiple rows. This is because the primary use of SQLGetData is to fetch long data in parts, and there is little or no reason to do this for more than one row at a time.
To use SQLGetData with a block cursor, an application first calls SQLSetPos to position the cursor on a single row. It then calls SQLGetData for a column in that row. However, this behavior is optional. To determine if a driver supports the use of SQLGetData with block cursors, an application calls SQLGetInfo with the SQL_GETDATA_EXTENSIONS option.