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SQL 7.0 Accessing Remote Data 
 


Added: 08/09/2002, Hits: 2,946, Rating: 0, Comments: 0, Votes: 0
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By Brian Talbert

This topic from the exam skills matrix lists a focus on linked servers. SQL Server 7.0 allows you to connect to remote data sources using either Remote Servers or Linked Servers. Remote Severs refer to a mechanism, also available in previous versions of SQL Server, that allows you to run remote stored procedures. This feature is still provided but considered a legacy feature. The new linked servers provide the same functionality plus a lot more.

So what are linked servers? They are essentially OLE DB data sources that can be referenced by T-SQL statements executing on the local server. Since they are OLE DB data sources, linked servers, are not limited to just SQL servers. They could be Oracle, Access, Excel, or other OLE DB sources. They enable you run remote stored procedures, just like Remote Servers, but also allow you to do a lot more, such as reference data on the linked server within a SELECT statement. You can even create a join that links the data between the local and remote data source, thus allowing for distributed queries.

When SQL Server attempts to connect to the linked server some sort of authentication information will need to be provided. By default, when a linked server is created, SQL Server sets it up so that the security credentials of the current user requesting the distributed query will be emulated. However, this may not work if the client does not allow account delegation of if the linked server does not support NT authentication mechanisms. If this is the case you must create a local login mapping. This is a pre-configured account and password that SQL Server will use when it attempts to make the remote connection.





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