Linked Servers in SQL Server

Outline of the Article: 

1. Introduction

A. Brief explanation of linked servers in SQL Server

B. Importance and benefits of using linked servers

2. Advantages and Disadvantages of Linked Servers

A. Advantages:

1. Improved data integration and consolidation

2. Seamless querying across multiple servers

3. Access to heterogeneous data sources

B. Disadvantages:

1. Security considerations

2. Performance impact

3. Complexity in configuration and maintenance

3. Benefits of Using Linked Servers

A. Streamlined data management and analysis

B. Enhanced reporting capabilities

C. Simplified cross-server queries and joins

4. Usage Scenarios for Linked Servers

A. Integration of data from different database systems

B. Accessing data from legacy systems

C. Federated queries across multiple servers

5. Step-by-Step Guide to Configure Linked Servers

A. Pre-requisites and considerations

B. Creating and configuring a linked server

C. Configuring security settings

D. Testing the linked server connection

6. Examples of Linked Server Queries

A. Retrieving data from a linked server

B. Performing joins across linked servers

C. Modifying data on a remote server

7. Common Issues/Problems we generally face with Linked Server

8. Conclusion

A. Recap of the advantages and benefits of using linked servers

B. Encouragement to explore and utilize linked servers in SQL Server

9. FAQs

A. Common questions and answers about linked servers in SQL Server

I. Introduction:

An effective way to access and combine data from several servers and data sources is through the use of linked servers in SQL Server. This detailed manual includes a step-by-step configuration approach as well as an examination of the advantages, benefits, and possible applications of connected servers. Understanding connected servers may greatly improve your data management abilities, whether you're trying to consolidate data, run cross-server queries, or access legacy systems.

Benefits and Drawbacks of Linked Servers: 

The benefits of linked servers include greater data integration, easy querying, and access to diverse data sources. However, they also have drawbacks including security risks, performance impacts, and configuration and upkeep complexity.

Benefits of Using Linked Servers: Using linked servers in SQL Server has advantages including improved reporting features, simpler data administration, and easier cross-server queries and joins. These benefits enable businesses to make wise decisions based on connected and aggregated data.

Utilisation Cases for Linked Servers:

Accessing data from historical systems, integrating data from various database systems, and running federated queries across numerous servers are all made possible by linked servers. Utilizing this, businesses may get rid of data silos and get a comprehensive picture of their data landscape.

How to Configure Linked Servers Step by Step:

A thorough explanation of the configuration procedure for connected servers is provided in this section. To enable flawless data integration, it covers requirements, installing and configuring a connected server, setting up security, and testing the connection.

1. Launch SQL Server Management Studio and join the SQL Server instance where the connected server will be created.

2. In the Object Explorer, open the Server Objects folder. Then, expand the Linked Servers folder by clicking on it once and choosing "New Linked Server." A dialogue box titled "New Linked Server" will now display.

3. General Qualities

a. A unique name should be entered for the associated server.

b. Server type: Opt for a reliable server, such as SQL Server or Oracle.

c. Choosing the right provider for the associated server type is option c.

d. Enter the name or network address of the associated server for the data source.

4. Security Constraints

a. Be made using this security context: use this option if we want to use a specific security context during the linked server connection.

b. Remote login: Put the remote login used to connect to the linked server.

c. With password: Put the password for the remote login.

5. Server Options:

a. RPC: We use this property to Allow or disallow RPC - Remote Procedure Call functionality.

b. RPC Out: We use this property to Allow or disallow RPC functionality for outgoing requests.

c. Use Remote Collation: Specify this property if we want to use the collation of the remote server.

d. Collation Compatible: Determines whether the collations of the local and remote servers are compatible or not.

e. Data Access: We use this property to Allow or disallow the linked server for data access.

f. Allow Remote Procedure Calls: We use this property to Allow or disallow the execution of remote procedures.

6. To build the associated server, click OK. It will show up in the Object Explorer's Linked Servers folder.

7. To set up the connected server's authentication, open the newly formed linked server, right-click on "Security," and then choose "New Login Mapping." You'll see the "New Login Mapping" dialogue box.

8. Choose the remote login that will be used for authentication in the "Remote User" section.

9. Choose the local SQL Server login or create a new login for mapping in the "Local User" section.

10. To store the login mapping, click OK.

11. To check the linked server connection, open the server in the Object Explorer, right-click "Tables," and choose "Script Linked Server as" > "SELECT." A script to test the associated server connection will be produced as a result.

12. Examine the script, make any required modifications, then run it to check the connection.

Finally, the system will display Congratulations message.! In SQL Server 2019, you have successfully built a connected server. Now, within your SQL Server environment, you may access and query data from the remote server using the connected server.

Examples of Linked Server Queries: This section provides examples of querying and altering data from a linked server to show the practical use of linked servers. These examples will walk you through the procedure regardless of whether you need to receive data, conduct joins across servers, or edit data on a distant server.

Example 1: Fetch required data through a linked server:

SELECT *

FROM [OurLinkedServerName].[OurDBName].[OurSchemaName].[OurTableName]

The above query will return all rows and columns from the table using a linked server named [OurLinkedServerName].

Example 2: Fetch required data After Joining multiple tables using linked servers

SELECT *

FROM [OurLinkedServer1].[OurDatabase1].[OurSchema1].[OurTable1] AS T1

JOIN [OurLinkedServer2].[OurDatabase2].[OurSchema2].[OurTable2] AS T2

    ON T1.[OurColumn1] = T2.[OurColumn1]

The above query will join two tables, OurTable1 & OurTable2 on OurLinkedServer1 with OurTable2 on OurLinkedServer2 based on a common column [OurColumn1].

Example 3: Modify data of a particular table that is on a remote server

UPDATE [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurTableName]

SET [OurColumn1] = 'NewValue'

WHERE [OurCondition]

Example 4: Using a WHERE clause to retrieve data from a connected server

SELECT *

FROM [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurTableName] WHERE [OurColumn1] = 'Value'

Example 5: Executing a stored method on a connected server

EXEC [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurStoredProcedureName] @Parameter1 = 'Value'

Example 6: Filling a table on a connected server with data

INSERT INTO [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurTableName] ([OurColumn1], [OurColumn2])

VALUES ('Value1', 'Value2')

Example 7: Erasing information out of a table on a connected server

DELETE FROM [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurTableName] WHERE [OurCondition]

Example 8: Executing a dynamic query on a connected server

DECLARE @OurDynamicSQL NVARCHAR(MAX)

SET @OurDynamicSQL = 'SELECT * FROM [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurTableName]'

EXEC (@DynamicSQL)

Example 9: Using a connected server alias to retrieve data from a distant table

SELECT *

FROM [OurLinkedServerAlias].[OurDatabaseName].[OurSchemaName].[OurTableName]

Example 10: Using an alias to join tables across connected servers

SELECT *

FROM [OurLinkedServer1].[OurDatabase1].[OurSchema1].[OurTable1] AS T1

JOIN [OurLinkedServer2].[OurDatabase2].[OurSchema2].[OurTable2] AS T2

    ON T1.[OurColumn1] = T2.[OurColumn1]

Example 11: Running a stored procedure with parameters on a connected server

EXEC [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurStoredProcedureName] @Parameter1 = 'Value1', @Parameter2 = 'Value2'

Example 12: Running a query on a connected server using OPENQUERY

SELECT *

FROM OPENQUERY([OurLinkedServerName], 'SELECT * FROM [OurDatabaseName].[OurSchemaName].[OurTableName]')

Example 13: Using a connected server and a WHERE clause to retrieve data from a distant server

 

SELECT *

FROM [OurLinkedServerName].[OurDatabaseName].[OurSchemaName].[OurTableName]

WHERE [OurColumn1] LIKE 'Value%'

Note: Replace [OurLinkedServerName], [OurDatabaseName], [OurSchemaName], [OurTableName], [OurColumn1], and [OurCondition] with our actual names and conditions.

Common Issues/Problems we generally face with Linked Server:

1. Check the Authentication Settings: Examine the Authentication Preferences: Check to see that the associated server authentication settings are set up properly. To access the remote server, confirm that the security context used for the associated server login has the required rights.

2. Firewall and Port Settings: Check that the required ports are open on both the local and distant servers' firewalls and port settings. Make that the firewall settings permit incoming and outgoing connections on the necessary ports by checking the firewall settings.

3. Remote Server Access: Access to a distant server: Verify that the remote server accepts connections from the local server's IP address or hostname. There may occasionally be IP-based access limitations on the remote server that need to be appropriately set.

4. Linked Server Provider Settings: Verify that the linked server's provider settings are set up correctly. Different provider choices would need to be used depending on the kind of remote server (SQL Server, Oracle, etc.). Verify the provider settings a second time to be sure they are correct.

5. Issues with permissions: Verify the permissions for the connected server login. Make that the login has access to the database objects and remote server that it needs to access. To fix any permission-related problems, provide the necessary permissions.

6. Network Connectivity: Confirm the local and distant servers' networks are connected. Verify that there are no network-related difficulties that can hinder establishing a connection to the remote server, such as network outages or connectivity issues.

7. TCP/IP and Named Pipes Protocols: Verify that Named Pipes and TCP/IP are enabled and properly configured on both the local and distant servers by using SQL Server Configuration Manager. The SQL Server services might need to be restarted to enable these protocols.

8. Authentication Mode: Verify that the Windows accounts have the right access rights to the distant server if the connected server utilizes Windows Authentication. Make that the login credentials are accurate and have the right permissions if SQL Server Authentication is being utilized.

9. Data Source Name (DSN): Verify the Data Source Name (DSN) settings if the associated server makes use of an ODBC connection. Make that the DSN is set up correctly with the necessary server, driver, and authentication information.

10. Testing the Connection: To test the connection to the associated server, use SQL Server Management Studio (SSMS) or SQL Server Management Objects (SMO). This might assist in locating any particular error messages or connection-related problems.

We should be able to address the majority of difficulties with linked server connections in SQL Server by troubleshooting these typical problems.

Conclusion:

SQL Server's linked servers provide a flexible and effective method for integrating and accessing data from many servers and data sources. We may make use of linked servers' capabilities and open up new options for data management and analysis by following the instructions provided in this tutorial.

FAQs

Q: Is the security of the connected servers guaranteed?

Ans. If improperly configured, linked servers might provide a security concern. Best practices should be adhered to, such as restricting access rights and employing secure authentication techniques.

Q: How do connected servers affect performance?

Ans. Executing cross-server queries might be affected by linked servers, notably in terms of speed. Considerations should be made for variables like network latency and data transfer volume. Performance difficulties can be reduced by optimizing network infrastructure and queries.

Q: Using connected servers, can I query many database systems?

Ans: Linked servers do really make it possible to query and retrieve data from several database systems, including Microsoft SQL Server, Oracle, MySQL, and others. Data retrieval and smooth interaction between various systems are made possible.

Q: What are the typical difficulties encountered while setting connected servers?

Ans: Authentication configuration, guaranteeing backward compatibility across connected servers and SQL Server versions, addressing firewall or network connectivity difficulties, and security management are some common obstacles. To address these difficulties, careful planning and environmental awareness are necessary.

Q: Can I use connected servers to alter data on a distant server?

Ans: Yes, connected servers enable dispersed queries to modify data on a remote server. Being cautious and making sure the right permissions and data integrity measures are in place are essential.

Q: Is it possible to employ connected servers for real-time data synchronization?

Ans: Linked servers basically make it easier to access and query data from distant servers. Other solutions, like replication or ETL procedures, are often more suited for real-time data synchronization.

Q: Can connected servers access data sources other than SQL Server?

Ans: Yes, connected servers allow connections to Oracle, MySQL, PostgreSQL, and ODBC-compliant databases in addition to SQL Server. This adaptability allows for system integration and querying across several platforms.

Q: The utilization of connected servers across several network domains is possible, right?

Ans: Yes, connected servers can be set up to communicate across several network domains, but doing so needs the right network setup, trust relationships, and permissions.

Q: Are on-premises setups the only ones that support networked servers?

Ans: In both on-premises and cloud contexts, connected servers can be employed. However, when dealing with cloud-based connected servers, factors such as network connection, security, and firewall setups may differ.

Q: Can data from legacy systems be accessed via connected servers?

Ans: To integrate with contemporary databases and applications for improved data utilization and decision-making, connected servers might be a useful tool for gaining access to data from outdated systems.