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Create Linked Servers (SQL Server Database Engine)

This topic shows how to create a linked server and access data from another SQL Server by using SQL Server Management Studio or Transact-SQL. By creating a linked server, you can work with data from multiple sources. The linked server does not have to be another instance of SQL Server, but that is a common scenario.

A linked server allows for access to distributed, heterogeneous queries against OLE DB data sources. After a linked server is created, distributed queries can be run against this server, and queries can join tables from more than one data source. If the linked server is defined as an instance of SQL Server, remote stored procedures can be executed.

The capabilities and required arguments of the linked server can vary significantly. The examples in this topic provide a typical example but all options are not described. For more information, see sp_addlinkedserver (Transact-SQL).

Permissions

When using Transact-SQL statements, requires ALTER ANY LINKED SERVER permission on the server or membership in the setupadmin fixed server role. When using Management Studio requires CONTROL SERVER permission or membership in the sysadmin fixed server role.

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You can use any of the following:

Using SQL Server Management Studio

To create a linked server to another instance of SQL Server Using SQL Server Management Studio

  1. In SQL Server Management Studio, open Object Explorer, expand Server Objects, right-click Linked Servers, and then click New Linked Server.

  2. On the General page, in the Linked server box, type the name of the instance of SQL Server that you area linking to.

    SQL Server

    Identify the linked server as an instance of Microsoft SQL Server. If you use this method of defining a SQL Server linked server, the name specified in Linked server must be the network name of the server. Also, any tables retrieved from the server are from the default database defined for the login on the linked server.

    Other data source

    Specify an OLE DB server type other than SQL Server. Clicking this option activates the options below it.

    Provider

    Select an OLE DB data source from the list box. The OLE DB provider is registered with the given PROGID in the registry.

    Product name

    Type the product name of the OLE DB data source to add as a linked server.

    Data source

    Type the name of the data source as interpreted by the OLE DB provider. If you are connecting to an instance of SQL Server, provide the instance name.

    Provider string

    Type the unique programmatic identifier (PROGID) of the OLE DB provider that corresponds to the data source. For examples of valid provider strings, see sp_addlinkedserver (Transact-SQL).

    Location

    Type the location of the database as interpreted by the OLE DB provider.

    Catalog

    Type the name of the catalog to use when making a connection to the OLE DB provider.

    To test the ability to connect to a linked server, in Object Explorer, right-click the linked server and then click Test Connection.

    Note Note

    If the instance of SQL Server is the default instance, enter the name of the computer that hosts the instance of SQL Server. If the SQL Server is a named instance, enter the name of the computer and the name of the instance, such as Accounting\SQLExpress.

  3. In the Server type area, select SQL Server to indicate that that the linked server is another instance of SQL Server.

  4. On the Security page, specify the security context that will be used when the original SQL Server connects to the linked server. In a domain environment where users are connecting by using their domain logins, selecting Be made using the login’s current security context is often the best choice. When users connect to the original SQL Server by using a SQL Server login, the best choice is often to select By using this security context, and then providing the necessary credentials to authenticate at the linked server.

    Local login

    Specify the local login that can connect to the linked server. The local login can be either a login using SQL Server Authentication or a Windows Authentication login. Use this list to restrict the connection to specific logins, or to allow some logins to connect as a different login.

    Impersonate

    Pass the username and password from the local login to the linked server. For SQL Server Authentication, a login with the exact same name and password must exist on the remote server. For Windows logins, the login must be a valid login on the linked server.

    To use impersonation, the configuration must meet the requirement for delegation.

    Remote User

    Use the remote user to map users not defined in Local login. The Remote User must be a SQL Server Authentication login on the remote server.

    Remote Password

    Specify the password of the Remote User.

    Add

    Add a new local login.

    Remove

    Remove an existing local login.

    Not be made

    Specify that a connection will not be made for logins not defined in the list.

    Be made without using a security context

    Specify that a connection will be made without using a security context for logins not defined in the list.

    Be made using the login's current security context

    Specify that a connection will be made using the current security context of the login for logins not defined in the list. If connected to the local server using Windows Authentication, your windows credentials will be used to connect to the remote server. If connected to the local server using SQL Server Authentication, login name and password will be used to connect to the remote server. In this case a login with the exact same name and password must exist on the remote server.

    Be made using this security context

    Specify that a connection will be made using the login and password specified in the Remote login and With password boxes for logins not defined in the list. The remote login must be a SQL Server Authentication login on the remote server.

  5. Optionally, to view or specify server options, click the Server Options page.

    Collation Compatible

    Affects Distributed Query execution against linked servers. If this option is set to true, SQL Server assumes that all characters in the linked server are compatible with the local server, with regard to character set and collation sequence (or sort order). This enables SQL Server to send comparisons on character columns to the provider. If this option is not set, SQL Server always evaluates comparisons on character columns locally.

    This option should be set only if it is certain that the data source corresponding to the linked server has the same character set and sort order as the local server.

    Data Access

    Enables and disables a linked server for distributed query access.

    RPC

    Enables RPC from the specified server.

    RPC Out

    Enables RPC to the specified server.

    Use Remote Collation

    Determines whether the collation of a remote column or of a local server will be used.

    If true, the collation of remote columns is used for SQL Server data sources, and the collation specified in collation name is used for non-SQL Server data sources.

    If false, distributed queries will always use the default collation of the local server, while collation name and the collation of remote columns are ignored. The default is false.

    Collation Name

    Specifies the name of the collation used by the remote data source if use remote collation is true and the data source is not a SQL Server data source. The name must be one of the collations supported by SQL Server.

    Use this option when accessing an OLE DB data source other than SQL Server, but whose collation matches one of the SQL Server collations.

    The linked server must support a single collation to be used for all columns in that server. Do not set this option if the linked server supports multiple collations within a single data source, or if the linked server's collation cannot be determined to match one of the SQL Server collations.

    Connection Timeout

    Time-out value in seconds for connecting to a linked server.

    If 0, use the sp_configure default remote query timeout option value.

    Query Timeout

    Time-out value in seconds for queries against a linked server.

    If 0, use the sp_configure default query wait option value.

    Enable Promotion of Distributed Transactions

    Use this option to protect the actions of a server-to-server procedure through a Microsoft Distributed Transaction Coordinator (MS DTC) transaction. When this option is TRUE, calling a remote stored procedure starts a distributed transaction and enlists the transaction with MS DTC. For more information, see sp_serveroption (Transact-SQL).

  6. Click OK.

To view the provider options

  • To view the options that the provider makes available, click the Providers Options page.

    All providers do not have the same options available. For example, some types of data have indexes available and some might not. Use this dialog box to help SQL Server understand the capabilities of the provider. SQL Server installs some common data providers, however when the product providing the data changes, the provider installed by SQL Server might not support all the newest features. The best source of information about the capabilities of the product providing the data is the documentation for that product.

    Dynamic parameter

    Indicates that the provider allows '?' parameter marker syntax for parameterized queries. Set this option only if the provider supports the ICommandWithParameters interface and supports a '?' as the parameter marker. Setting this option allows SQL Server to execute parameterized queries against the provider. The ability to execute parameterized queries against the provider can result in better performance for certain queries.

    Nested queries

    Indicates that the provider allows nestedSELECT statements in the FROM clause. Setting this option allows SQL Server to delegate certain queries to the provider that require nesting SELECT statements in the FROM clause.

    Level zero only

    Only level 0 OLE DB interfaces are invoked against the provider.

    Allow inprocess

    SQL Server allows the provider to be instantiated as an in-process server. When this option is not set, the default behavior is to instantiate the provider outside the SQL Server process. Instantiating the provider outside the SQL Server process protects the SQL Server process from errors in the provider. When the provider is instantiated outside the SQL Server process, updates or inserts referencing long columns (text, ntext, or image) are not allowed.

    Non transacted updates

    SQL Server allows updates, even if ITransactionLocal is not available. If this option is enabled, updates against the provider are not recoverable, because the provider does not support transactions.

    Index as access path

    SQL Server attempts to use indexes of the provider to fetch data. By default, indexes are used only for metadata and are never opened

    Disallow ad hoc access

    SQL Server does not allow ad hoc access through the OPENROWSET and OPENDATASOURCE functions against the OLE DB provider. When this option is not set, SQL Server also does not allow ad hoc access.

    Supports 'Like' operator

    Indicates that the provider supports queries using the LIKE key word.

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Using Transact-SQL

To create a linked server by using Transact-SQL, use the sp_addlinkedserver (Transact-SQL)CREATE LOGIN (Transact-SQL) and sp_addlinkedsrvlogin (Transact-SQL) statements.

To create a linked server to another instance of SQL Server using Transact-SQL

  1. In Query Editor, enter the following Transact-SQL command to link to an instance of SQL Server named SRVR002\ACCTG:

    USE [master]
    GO
    EXEC master.dbo.sp_addlinkedserver 
        @server = N'SRVR002\ACCTG', 
        @srvproduct=N'SQL Server' ;
    GO
    
  2. Execute the following code to configure the linked server to use the domain credentials of the login that is using the linked server.

    EXEC master.dbo.sp_addlinkedsrvlogin 
        @rmtsrvname = N'SRVR002\ACCTG', 
        @locallogin = NULL , 
        @useself = N'True' ;
    GO
    

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To test the linked server

  • Execute the following code to test the connection to the linked server. This example the returns the names of the databases on the linked server.

    SELECT name FROM [SRVR002\ACCTG].master.sys.databases ;
    GO
    

Writing a query that joins tables from a linked server

  • Use four-part names to refer to an object on a linked server. Execute the following code to return a list of all logins on the local server and their matching logins on the linked server.

    SELECT local.name AS LocalLogins, linked.name AS LinkedLogins
    FROM master.sys.server_principals AS local
    LEFT JOIN [SRVR002\ACCTG].master.sys.server_principals AS linked
        ON local.name = linked.name ;
    GO
    

    When NULL is returned for the linked server login it indicates that the login does not exist on the linked server. These logins will not be able to use the linked server unless the linked server is configured to pass a different security context or the linked server accepts anonymous connections.

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