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Q173410: INFO: Server-Side Cursors Are Forced w/More Than One Command Obj

Article: Q173410
Product(s): Open Database Connectivity (ODBC)
Version(s): 1.1
Operating System(s): 
Keyword(s): kbprogramming kbODBC kbOLEDB
Last Modified: 19-JUL-2001

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The information in this article applies to:

- Microsoft OLE DB, version 1.1 
- Microsoft OLE DB Provider for ODBC, version 1.1 
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SUMMARY
=======

The OLE DB Provider for ODBC may force the use of server-side cursors if both of
the following conditions are true:

- The backend database server is Microsoft SQL Server.

  -and-

- More than one Command object exists within the same session object.

Server-side cursors will be implicitly forced with any queries, even they are if
not requested by the application.

MORE INFORMATION
================

The Microsoft SQL Server ODBC driver can have only one active statement unless
server-side cursors are used. An ODBC application may receive the following
error message if it attempts to have more than one active statement without
using server-side cursors:

  szSqlState = "S1000", *pfNativeError = 0
  szErrorMsg = "[Microsoft][ODBC SQL Server Driver]Connection is busy with
  results for another hstmt"

Using the OLE DB Provider for ODBC, an OLE DB application is like an ODBC
application. The OLE DB Provider for ODBC translates OLE DB interface requests
into ODBC APIs, and then sends ODBC requests to ODBC drivers. OLE DB session
objects are mapped to ODBC connections, and command objects are mapped to
statements.

Dealing with the SQL Server ODBC driver, the OLE DB Provider for ODBC forces the
use of server-side cursors if there is more than one command object or statement
opened. With more than one command object or statement opened, the application
may run into the one active statement limitation. Therefore, the OLE DB Provider
for ODBC automatically uses server-side cursors to avoid the limitation. The
type of server-side cursor enforced by the ODBC Provider is forward-only and
read-only. For example, the forward and read-only server-side cursors will be
forced with the following code:

     IcommandText         *pICommandText1;
     IcommandText         *pICommandText1;
     Icommand             *pIDBCommand;
     WCHAR  *stmt_string = SysAllocString((LPOLESTR)L"SELECT * FROM TITLES");

     ...connect to the OLE DB Provider for ODBC, create session and command object .....

     pIDBCommand-
     >CreateCommand(NULL,IID_ICommandText,(IUnknown**)&pICommandText1)
     pIDBCommand-
     >CreateCommand(NULL,IID_ICommandText,(IUnknown**)&pICommandText2)

     pICommandText1->SetCommandText ( DBGUID_DBSQL,  stmt_string )
     pICommandText1->Execute(NULL, IID_NULL, NULL, NULL,NULL)

With server-side cursors being enforced, an application cannot execute SQL
statements that generate more than one resultset. SQL Server only allows
executing server-side cursors with SQL statements that generate a single
resultset. At this point, the application will have to release all the command
objects except one, so that server-side cursor will not be enforced. Then the
multiple-resultset SQL statements can be executed successfully.

For additional information for server-side cursors and multiple resultsets,
please see the following article in the Microsoft Knowledge Base:

  Q156500 INF: Processing Procedures and Batches with Multiple SELECTS

Additional query words: busy oledb

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Keywords          : kbprogramming kbODBC kbOLEDB 
Technology        : kbAudDeveloper kbODBCSearch kbOLEDBSearch kbOLEDB110 kbOLEDBProvODBC110 kbOLEDBProvSearch
Version           : :1.1
Issue type        : kbinfo

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