Disconnecting from a Data Source
SQL Server Native Client (SNAC) is not supported beyond SQL Server 2012. Avoid using SNAC in new development work, and plan to modify applications that currently use it. The Microsoft ODBC Driver for SQL Server provides native connectivity from Windows to Microsoft SQL Server and Microsoft Azure SQL Database.
When an application has finished using a data source, it calls SQLDisconnect. SQLDisconnect frees any statements that are allocated on the connection and disconnects the driver from the data source. After disconnecting, the application can call SQLFreeHandle to free the connection handle. Before exiting, an application also calls SQLFreeHandle to free the environment handle.
After disconnecting, an application can reuse the allocated connection handle, either to connect to a different data source or reconnect to the same data source. The decision to remain connected instead of disconnecting and reconnecting later requires that the application writer consider the relative costs of each option. Connecting to a data source and remaining connected can be relatively costly, depending on the connection medium. In making a trade-off, the application must also make assumptions about the probability and timing of additional operations on the same data source. An application may also have to use more than one connection.