Three types of changes are made in ODBC 3.x (and any version of ODBC). Each of these affects backward compatibility differently and is handled in a different way. These changes are as follows:
| Type of change | Description |
| New features | These are features that are new to ODBC 3.x, such as out-of-line binding or descriptors. These are only implemented when the application and driver, as well as the Driver Manager, are of version 3.x, so there is no attempt to make these backward compatible. |
| Duplicated features | These are features that exist in both ODBC 2.x and ODBC 3.x, but are implemented in different ways in both. The functions SQLAllocHandle and SQLAllocStmt are an example. Backward compatibility issues for these and other duplicated features are mostly handled by mappings in the Driver Manager. |
| Behavioral changes | These are features that are handled differently in ODBC 2.x and ODBC 3.x. A datetime #define is an example. These features are handled by the ODBC 3.x driver based on an environment attribute setting (see the "Behavioral Changes" section later in this chapter). |