DOCUMENT:Q149054 11-JAN-2001 [vbwin] TITLE :INFO: Choosing an rdoResultset Cursortype PRODUCT :Microsoft Visual Basic for Windows PROD/VER:WINDOWS:4.0,5.0 OPER/SYS: KEYWORDS:kbGrpDSVBDB ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Professional Edition for Windows, version 5.0 - Microsoft Visual Basic Enterprise Edition for Windows, version 5.0 - Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 ------------------------------------------------------------------------------- SUMMARY ======= This article describes the types of rdoResultset cursors in RDO and when to use them. NOTE: The following text comes directly from the Visual Basic online Help. Because there are no hot-links to the online Help, you must search for information explicitly. Go into Help, click on the Search button, click on the Find tab, type in Cursors, and then select Choosing a cursor type. MORE INFORMATION ================ Choosing the right cursor for an application impacts performance and resource management. Your choice of cursor depends on how many rows you intend to access, how you need to navigate through the result set, how membership is determined, and how you intend to update the data. In many cases, use of the forward-only type result set is the best choice as it exposes only one row of the result set at a time and is far easier for RDO to create. However, it is not a cursor and does not permit access to more than one row at a time. 1. Server-Side Cursor Support An important aspect of keyset or dynamic cursors is where the keyset is created. If the server supports server-side cursors, as with Microsoft SQL Server 6.0 and above, you can specify that the cursor keyset is created and maintained on the server. 2. Selecting a Cursor Type To select a specific type of rdoResultset cursor, set the RemoteData control's ResultsetType property or the type argument of the OpenResultset method to: Resultset type Constant ------------------------------------------- Forward-only (Default) rdOpenForwardOnly Static rdOpenStatic Keyset rdOpenKeyset Dynamic rdOpenDynamic 3. Available Cursor Types The following table summarizes the four types of rdoResultset cursors: Attribute Forward-only Static Keyset Dynamic ------------------------------------------------------------- Updatable Yes (SS) No (SS) Yes Yes No (CL) Yes (CL) Membership Fixed Fixed Fixed Dynamic Visibility One row Cursor Cursor Cursor Move current row Forward Anywhere Anywhere Anywhere Result of a join Yes Yes Yes Yes NOTE: CL indicates that support for this cursor is provided by the ODBC cursor library. SS indicates support by Microsoft SQL Server. Choose the type of rdoResultset object to create by using the type argument of the OpenResultset method or the ResultsetType property of the RemoteData control. If a type is not specified, the RemoteData control creates a keyset-type rdoResultset. When using RDO to create rdoResultset objects, the default type is forward-only. 4. Supported Cursor Types Not all data sources support every type of cursor. The following table summarizes which type of cursor is supported on several typical data sources and on the RemoteData control: Data source Forward-only Static Keyset Dynamic ------------------ ------------ ------- ------ ------- SQL Server 4.2 Yes Yes/CL No No SQL Server 6.0 and above Yes Yes Yes Yes Oracle 7.1 Yes Yes/CL No No RemoteData control No es Yes/DD No NOTE: CL indicates that support for this cursor is provided by the ODBC cursor library. DD indicates support is provided subject to support by the ODBC driver. 5. Cursors and the RemoteData Control Creating an rdoResultset and setting the Resultset property with this new object sets the ResultsetType property of the RemoteData control to the Type property of the new rdoResultset. NOTE: When using forward-only, read-only result sets, the rdoConnection is held open until the last row of data is accessed. While this can provide performance improvements over other cursors, it can also tie up connection resources. REFERENCES ========== Visual Basic online Help Building Client/Server Applications with Visual Basic Hitchhiker's Guide to Visual Basic and SQL Server, Microsoft Press. ISBN: 1-55615-906-4. 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