MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 8: SQL Statements
When calling procedures that accept parameters, interoperable applications should use parameter markers instead of literal parameter values. Some data sources do not support the use of literal parameter values in procedure calls. For more information about parameters, see "Statement Parameters" in Chapter 9, "Executing Statements." For more information about calling procedures, see "Procedure Calls," later in this chapter.