openrowset,

openrowset
Includes all connection information necessary to access remote data from an OLE DB data source. This method is an alternative to accessing tables in a linked server and is a one-time, ad hoc method of connecting and accessing remote data using OLE DB. The OPENROWSET function can be referenced in the FROM clause of a query as though it is a table name. The OPENROWSET function can also be referenced as the target table of an INSERT, UPDATE, or DELETE statement, subject to the capabilities of the OLE DB provider. Although the query may return multiple result sets, OPENROWSET returns only the first one.

opendatasource

The OPENDATASOURCE function can be used in the same Transact-SQL syntax locations as a linked server name. Thus, OPENDATASOURCE can be used as the first part of a four-part name that refers to a table or view name in a SELECT, INSERT, UPDATE, or DELETE statement, or to a remote stored procedure in an EXECUTE statement. When executing remote stored procedures, OPENDATASOURCE should refer to another SQL Server. OPENDATASOURCE does not accept variables for its arguments.

Like the OPENROWSET function, OPENDATASOURCE should only reference OLE DB data sources accessed infrequently. Define a linked server for any data sources accessed more than a few times. Neither OPENDATASOURCE, nor OPENROWSET provide all the functionality of linked server definitions, such as security management and the ability to query catalog information. All connection information, including passwords, must be provided each time OPENDATASOURCE is called.

SELECT   * FROM      OPENDATASOURCE(          'SQLOLEDB',          'Data Source=ServerName;User ID=MyUID;Password=MyPass'          ).Northwind.dbo.Categories

openquery
Executes the specified pass-through query on the given linked server, which is an OLE DB data source. The OPENQUERY function can be referenced in the FROM clause of a query as though it is a table name. The OPENQUERY function can also be referenced as the target table of an INSERT, UPDATE, or DELETE statement, subject to the capabilities of the OLE DB provider. Although the query may return multiple result sets, OPENQUERY returns only the first one.

EXEC sp_addlinkedserver 'OracleSvr',     'Oracle 7.3',     'MSDAORA',     'ORCLDB' GO SELECT * FROM OPENQUERY(OracleSvr, 'SELECT name, id FROM joe.titles')  GO