This appendix provides information for driver writers working on ODBC 3.0 drivers that need to support ODBC 2.x applications. Changes between ODBC 2.x and ODBC 3.0 fall into three categories; for more information about these categories, see “Backward Compatibility and Standards Compliance” in Chapter 17, “Programming Considerations.”
New Features. New features are features that exist in ODBC 3.0 and not in ODBC 2.x. ODBC 3.0 drivers generally do not have to worry about backward compatibility
with new features because ODBC 2.x applications never use it. The sole exception to this is features related to SQLFetch, SQLFetchScroll, SQLSetPos, and SQLExtendedFetch; for more information, see “Block Cursors, Scrollable Cursors, and Backward Compatibility,” later in this appendix.
Duplicated Features. Duplicated features are features that are implemented differently in ODBC
3.0 and ODBC 2.x. ODBC 3.0 drivers do not have to worry about backward compatibility with
duplicated features because the Driver Manager always maps ODBC 2.x features to ODBC 3.0 features when calling an ODBC 3.0 driver. Thus, an ODBC
3.0 driver sees only ODBC 3.0 features. For more information about these
mappings, see
Behavioral Changes. Behavior changes are features that are handled differently in ODBC 3.0 and
ODBC 2.x. ODBC 3.0 drivers have to worry about behavior changes and act in response to
the SQL_ATTR_ODBC_VERSION environment attribute set by the application. For
more information, see