Create Link Server Sql Server

Understanding Linked Servers in SQL Server

Linked Servers in SQL Server are a powerful feature that allows for seamless data integration across different database systems. This functionality enables a SQL Server instance to execute commands against OLE DB data sources on remote servers. Essentially, it allows for cross-server communication, enabling queries that can join tables from different servers as if they were located on the same server.

Benefits of Using Linked Servers

Remote Data Access: Access data from other SQL Server instances or heterogeneous data sources like Oracle, Excel, Access, and more.
Distributed Queries: Execute queries that combine data from multiple data sources.
Transactional Support: Perform transactions across multiple databases with distributed transactions.
Easy Management: Manage and access multiple data sources through a single SQL Server interface.

Types of Data Sources You Can Link To

Other SQL Server instances
Oracle databases
Microsoft Access databases
Excel spreadsheets
Flat files
Other OLE DB-compliant data sources

Setting Up a Linked Server

Creating a linked server involves several steps, from choosing the right provider to configuring security settings. The process can be done using SQL Server Management Studio (SSMS) or through T-SQL commands.

Using SQL Server Management Studio (SSMS)

To create a linked server via SSMS, follow these steps:

Open SSMS and connect to the instance where you want to create the linked server.
Navigate to ‘Server Objects’, then ‘Linked Servers’, and right-click to select ‘New Linked Server’.
Provide the linked server name, select the provider, and set the product name and data source.
Configure the security settings to determine how authentication will be handled.
After setting the options, click ‘OK’ to create the linked server.

Using T-SQL Commands

Alternatively, you can create a linked server using T-SQL with the sp_addlinkedserver and sp_addlinkedsrvlogin stored procedures. Here’s an example of how to create a linked server to another SQL Server instance:


EXEC sp_addlinkedserver
    @server='LINKEDSERVERNAME',
    @srvproduct='',
    @provider='SQLNCLI', -- SQL Server Native Client
    @datasrc='TARGET_SERVER_NAME'; -- The name of the target server

EXEC sp_addlinkedsrvlogin
    @rmtsrvname='LINKEDSERVERNAME',
    @useself='FALSE',
    @locallogin=NULL,
    @rmtuser='RemoteUsername',
    @rmtpassword='RemotePassword';

This script sets up a linked server with explicit remote login credentials.

Querying Data from a Linked Server

Once a linked server is established, you can query data using the fully qualified name format, which includes the linked server name, database name, schema name, and table name.

Four-Part Naming Convention

Here’s an example of a SELECT statement using the four-part naming convention:


SELECT * FROM [LINKEDSERVERNAME].[DatabaseName].[SchemaName].[TableName];

This query retrieves all records from the specified table on the linked server.

Using OPENQUERY Function

Alternatively, you can use the OPENQUERY function to execute a pass-through query on the linked server. This can be more efficient as the query is executed on the remote server and only the result set is returned.


SELECT * FROM OPENQUERY(LINKEDSERVERNAME, 'SELECT * FROM DatabaseName.SchemaName.TableName');

Performance Considerations and Best Practices

When working with linked servers, it’s important to consider the performance implications and follow best practices to ensure efficient operations.

Performance Tips

Avoid using SELECT * in queries; instead, specify only the required columns.
Minimize data transfer by filtering data on the remote server using WHERE clauses.
Consider using OPENQUERY for complex queries to leverage the remote server’s processing power.
Regularly monitor and analyze query performance using execution plans and SQL Server Profiler.

Security Best Practices

Use secure login credentials and avoid storing plain text passwords.
Limit permissions on the remote server to only what is necessary for the queries.
Regularly review linked server connections and remove any that are no longer needed.
Implement encryption for sensitive data transfers, if supported by the data source.

Advanced Linked Server Configurations

Beyond basic setup, SQL Server offers advanced configurations for linked servers to handle specific scenarios and requirements.

Configuring Linked Servers for High Availability

For environments using high availability solutions like Always On Availability Groups, linked servers must be configured to handle failovers. This involves setting up linked servers to point to the availability group listener rather than individual server instances.

Linked Servers with SQL Server Replication

In replication scenarios, linked servers can be used to manage replication agents and monitor replication performance across different servers.

Troubleshooting Common Linked Server Issues

While linked servers are a powerful feature, they can sometimes present challenges. Common issues include connectivity problems, authentication errors, and query performance.

Connectivity and Authentication Problems

To resolve connectivity issues, verify network settings, firewalls, and ensure the remote server is accessible. For authentication errors, check login credentials and permissions.

Query Performance Tuning

If queries are running slow, consider indexing strategies, updating statistics, and reviewing query execution plans to identify bottlenecks.

Frequently Asked Questions

Can I create a linked server to a non-SQL Server database?

Yes, SQL Server can connect to various OLE DB-compliant data sources, including Oracle, Excel, and Access.

Is it possible to write data to a linked server?

Yes, you can perform INSERT, UPDATE, and DELETE operations on a linked server, provided you have the necessary permissions.

How do I secure my linked server connections?

Use secure login credentials, limit permissions, and consider implementing encryption for data transfers.

Can I use linked servers with Azure SQL Database?

Azure SQL Database supports outbound connections to linked servers, but inbound connections are not supported due to security reasons.

What are some alternatives to linked servers for data integration?

Alternatives include SQL Server Integration Services (SSIS), Azure Data Factory, and third-party ETL tools.

References

For further reading and in-depth understanding of linked servers in SQL Server, refer to the following resources: