FIX: Cursor Library Returns Duplicate Row in Asynchronous Mode

• Microsoft Open Database Connectivity, version 2.0

SYMPTOMS

When the ODBC Cursor Library is used to set up a static cursor with a driver whose asynchronous mode is enabled, it returns duplicate rows under certain circumstances. These duplicate rows are returned every time an asynchronous operation with the driver returns SQL_STILL_EXECUTING. The number of duplicate rows retrieved on subsequent fetches (MoveNext's in MFC) is variable. Certain conditions can cause as many as 500 consecutive repetitions of the same record.

This behavior has typically been observed in MFC applications using the ODBC database classes to build snapshots (which cause the ODBC Cursor Library's static cursor implementation to be used).

WORKAROUND

Users of MFC database classes can avert this behavior by:

1. Setting synchronous mode on by calling the SetSynchronousMode() method of CDatabase

2. Using forwardOnly recordsets

1. Calling SQLSetStmtOption (hstmt, SQL_ASYNC_ENABLE, SQL_ASYNC_ENABLE_OFF).

2. Using forward-only cursors in the Cursor Library.

STATUS

Microsoft has confirmed this to be a problem in ODBC Cursor Library version 2.00.1510. This problem has been fixed in the 32-bit version of the ODBC 2.5 Cursor Library (ODBCCR32.DLL, 2.50.3006). The 16-bit cursor library has not been changed. If you are using the 16 bit SQL Server driver, this should not be a problem because you can use the server side cursors in SQL Server version 6.0 and eliminate the need for the cursor library. If you are using the Access driver, you need to use the 32-bit driver and the new 32-bit cursor library.

MORE INFORMATION

You can get ODBC 2.50 components from:

• anonymous-FTP: FTP.MICROSOFT.COM:\BUSSYS\SQL_ODBC\ODBC-PUBLIC\ODBC25.EXE
• The Microsoft Developer Network (MSDN) Level II CD: ODBC210B\X86\ODBC25