MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 17: Programming Considerations

Connection Pooling Considerations

Performing any of the following actions using an SQL Command (rather than through the ODBC API) can affect the connection's state and cause unexpected problems when connection pooling is active:

• Opening a connection and changing the default database
  
  
• Using the SET statement to change any configurable options (including SET ROWCOUNT, ANSI_NULL, IMPLICIT_TRANSACTIONS, SHOWPLAN, STATISTICS, TEXTSIZE, and DATEFORMAT)
  
  
• Creating temporary tables and stored procedures

If any of these actions are performed outside of the ODBC API, the next person who uses the connection will automatically inherit the previous settings, tables, or procedures.

Note   Do not expect certain settings to be present in the connection state. You should always set the connection state in your application and ensure that the application removes any unused connection pooling settings.