Accessing Data from Multiple SQL Servers

In many scenarios, database administrators and developers need to access data from multiple SQL Server instances, which can be located on different servers. This can be achieved by using a feature called Linked Servers in SQL Server. In this tutorial, we will explore how to set up Linked Servers and use them to query data from multiple servers.

What are Linked Servers?

Linked Servers are a feature in SQL Server that allows you to access data from other SQL Server instances or other database products such as Oracle. This enables you to execute distributed queries, updates, commands, and transactions on heterogeneous data sources across the enterprise.

Benefits of Linked Servers

The benefits of using Linked Servers include:

• Ability to access data from outside of SQL Server
• Ability to issue distributed queries, updates, commands, and transactions on heterogeneous data sources
• Ability to address diverse data sources similarly

Creating a Linked Server

To create a Linked Server, follow these steps:

1. Open SQL Server Management Studio (SSMS) and navigate to the Object Explorer.
2. Expand the "Server Objects" folder and right-click on "Linked Servers".
3. Select "New Linked Server" from the context menu.
4. Provide the remote server name, select the remote server type (SQL Server or Other), and provide the login and password for the remote server.
5. Click OK to create the Linked Server.

Alternatively, you can use the sp_addlinkedserver stored procedure to create a Linked Server using T-SQL:

EXEC sp_addlinkedserver 
    @server = 'LinkedServerName', 
    @srvproduct = 'SQL Server', 
    @provider = 'SQLOLEDB', 
    @datasrc = 'RemoteServerName'

Querying Data from a Linked Server

Once you have created a Linked Server, you can query data from the remote server using a four-part name:

SELECT * FROM LinkedServerName.DatabaseName.OwnerName.TableName

Note that the owner is not always dbo, so make sure to replace it with the correct schema name.

Example Use Case

Suppose we have two SQL Server instances, Server1 and Server2, each containing a database called MyDatabase. We can create a Linked Server on Server1 to access data from Server2 as follows:

EXEC sp_addlinkedserver 
    @server = 'Server2', 
    @srvproduct = 'SQL Server', 
    @provider = 'SQLOLEDB', 
    @datasrc = 'Server2'

SELECT * FROM Server2.MyDatabase.dbo.MyTable

This allows us to query data from MyTable on Server2 from Server1.

Best Practices

When using Linked Servers, keep in mind the following best practices:

• Make sure to use the correct schema name when querying data from a Linked Server.
• Use the four-part name to specify the Linked Server, database, owner, and table.
• Be aware of the security implications of creating a Linked Server, as it allows access to data from outside of SQL Server.

By following these steps and best practices, you can easily set up Linked Servers and query data from multiple SQL Server instances.