Updating an Application to SQL Server Native Client from MDAC
There are a number of differences between SQL Server Native Client and Microsoft Data Access Components (MDAC; starting with Windows Vista, the data access components are now called Windows Data Access Components, or Windows DAC). Although both provide native data access to SQL Server databases, SQL Server Native Client has been specifically designed to expose the new features of SQL Server 2005, while at the same time maintaining backward compatibility with earlier versions.
The information in this topic helps update your MDAC (or Windows DAC) application to be current with the version of SQL Server Native Client that was included in SQL Server 2005. To help you make this application be current with the version of SQL Server Native Client that shipped in SQL Server 2008, see Updating an Application to SQL Server 2008 Native Client from SQL Server 2005 Native Client.
In addition, although MDAC contains components for using OLE DB, ODBC, and ActiveX Data Objects (ADO), SQL Server Native Client only implements OLE DB and ODBC (although ADO can access the functionality of SQL Server Native Client).
SQL Server Native Client and MDAC differ in the other following areas:
Users who use ADO to access a SQL Server Native Client provider may find less filtering functionality than when they accessed a SQL OLE DB provider.
If an ADO application uses SQL Server Native Client and attempts to update a computed column, an error will be reported. With MDAC the update was accepted but ignored.
SQL Server Native Client is a single self-contained dynamic link library (DLL) file. The publicly exposed interfaces have been kept to a minimum, both to ease distribution, as well as to limit security exposure.
Only OLE DB and ODBC interfaces are supported.
The SQL Server Native Client OLE DB provider and ODBC driver names are different from those used with MDAC.
User-accessible functionality supplied by MDAC components is available when using SQL Server Native Client. This includes, but is not limited to, the following: connection pooling, ADO support, and client cursor support. When any of these features are used, SQL Server Native Client supplies only database connectivity. MDAC provides functionality such as tracing, management controls, and performance counters.
Applications can use OLE DB core services with SQL Server Native Client, but if using the OLE DB cursor engine, they should use the data type compatibility option to avoid any potential problems that might arise because the cursor engine has no knowledge of the new SQL Server 2005 data types.
SQL Server Native Client supports access to previous SQL Server databases starting with SQL Server 7.0 and newer versions.
SQL Server Native Client does not contain XML integration. SQL Server Native Client supports SELECT … FOR XML queries, but does not support any other XML functionality. However, SQL Server Native Client does support the xml data type introduced in SQL Server 2005.
SQL Server Native Client supports configuring client-side network libraries using only connection string attributes. If you need more complete network library configuration, you must use SQL Server Configuration Manager.
SQL Server Native Client is not compatible with odbcbcp.dll. Applications that use both ODBC and bcp APIs must be rebuilt to link with sqlncli10.lib in order to use SQL Server Native Client.
SQL Server Native Client is not supported from the Microsoft OLE DB provider for ODBC (MSDASQL). If you are using the MDAC SQLODBC driver with MSDASQL or MDAC SQLODBC driver with ADO, use OLE DB in SQL Server Native Client..
MDAC connection strings allow a Boolean value (true) for the Trusted_Connection keyword. A SQL Server Native Client connection string must use yes or no.
Minor changes have occurred to warnings and errors. Warnings and errors returned by the server now retain the same severity when passed to SQL Server Native Client. You should ensure you have thoroughly tested your application if you depend on trapping particular warnings and errors.
SQL Server Native Client has stricter error checking than MDAC, which means that some applications that do not conform strictly to the ODBC and OLE DB specifications may behave differently. For example, the SQLOLEDB provider did not enforce the rule that parameter names must start with '@' for result parameters, but the SQL Server Native Client OLE DB provider does.
SQL Server Native Client behaves differently from MDAC in regards to failed connections. For example, MDAC returns cached property values for a connection that has failed, whereas SQL Server Native Client reports an error to the calling application.
SQL Server Native Client does not generate Visual Studio Analyzer events, but instead generates Windows tracing events.
SQL Server Native Client cannot be used with perfmon. Perfmon is a Windows tool that can only be used with DSNs that use the MDAC SQLODBC driver included with Windows.
When SQL Server Native Client is connected to SQL Server 2005, server error 16947 is returned as a SQL_ERROR. This error occurs when a positioned update or delete fails to update or delete a row. With SQL Server 2000 and earlier versions, and with MDAC when connecting to any version of SQL Server, server error 16947 is returned as a warning (SQL_SUCCESS_WITH_INFO).
SQL Server Native Client implements the IDBDataSourceAdmin interface, which is an optional OLE DB interface that was not previously implemented, but only the CreateDataSource method of this optional interface is implemented. This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.
The SQL Server Native Client OLE DB provider returns synonyms in the TABLES and TABLE_INFO schema rowsets, with TABLE_TYPE set to SYNONYM.
Return values of data type varchar(max), nvarchar(max), varbinary(max), xml, udt, or other large object types can not be returned to client versions earlier than SQL Server 2005. If you wish to use these types as return values, you must use SQL Server Native Client.
MDAC allows the following statements to be executed at the start of manual and implicit transactions, but SQL Server Native Client does not. They must be executed in autocommit mode.
All full-text operations (index and catalog DDL)
All database operations (create database, alter database, drop database)
When MDAC applications connect to SQL Server, the data types introduced in SQL Server 2005 will appear as SQL Server 2000-compatible data types as shown in the following table.
SQL Server 2005 type
SQL Server 2000 type
This type mapping affects the values returned for column metadata. For example, a text column has a maximum size of 2,147,483,647, but SQL Server Native Client ODBC reports the maximum size of varchar(max) columns as SQL_SS_LENGTH_UNLIMITED, and SQL Server Native Client OLE DB reports the maximum size of varchar(max) columns as 2,147,483,647 or -1, depending on platform.
SQL Server Native Client allows ambiguity in connection strings (for example, some keywords may be specified more than once, and conflicting keywords may be allowed with resolution based on position or precedence) for reasons of backward compatibility. Future releases of SQL Server Native Client might not allow ambiguity in connection strings. It is good practice when modifying applications to use SQL Server Native Client to eliminate any dependency on connection string ambiguity.
If you use an ODBC or OLE DB call to start transactions, there is a difference in behavior between SQL Server Native Client and MDAC; transactions will begin immediately with SQL Server Native Client, but transactions will begin after the first database access using MDAC. This can affect the behavior of stored procedures and batches because SQL Server requires @@TRANCOUNT to be the same after a batch or stored procedure finishes execution as it was when the batch or stored procedure started. See Rollbacks and Commits in Stored Procedures and Triggers for more information.
With SQL Server Native Client, ITransactionLocal::BeginTransaction will cause a transaction to be started immediately. With MDAC the transaction start was delayed until the application executed a statement which required a transaction in implicit transaction mode. For more information, see SET IMPLICIT_TRANSACTIONS (Transact-SQL).
You might encounter errors when using SQL Server Native Client driver with System.Data.Odbc to access a SQL Server server computer that exposes new, SQL Server-specific data types or features. System.Data.Odbc provides a generic ODBC implementation and subsequently does not expose vendor specific functionality or extensions. (The SQL Server Native Client driver is updated to natively support the latest SQL Server features.) To workaround this issue, you can either revert to MDAC, or migrate to System.Data.SqlClient.
Both SQL Server Native Client and MDAC support read committed transaction isolation using row versioning, but only SQL Server Native Client supports snapshot transaction isolation. (In programming terms, read committed transaction isolation using row versioning is the same as read-committed transaction.) For more information, see Choosing Row Versioning-based Isolation Levels.