A synonym is a database object that servers the purpose of providing an alternative name for another database object, referred to as the base object, that can exist on a local or remote server as well as the purpose of providing a layer of abstraction that protects a client application from changes made to the name or location of the base object.
A synonym belongs to a schema, and like other objects in a schema, the name of the synonym must be unique. References to synonyms are not schema-bound. Therefore, a synonym can be dropped at any time. However, dropping a synonym runs the risk of leaving dangling references to the synonym that was dropped. These references will only be found at run time.
One restriction when creating a synonym is that a synonym cannot be the base for another synonym, otherwise the following error message is generated:
Msg 470, Level 16, State 1, Line 1
The synonym "<Synonym Name>" referenced synonym "<Synonym Name>". Synonym chaining is not allowed.
To overcome this restriction and be able create a synonym that references another synonym indirectly is with the user of a view, as can be seen from the following script:
CREATE SYNONYM [dbo].[OldStudents] FOR [SchoolArchive].[dbo].[Students]
CREATE VIEW [dbo].[OldStudents2]
SELECT * FROM [dbo].[OldStudents]
CREATE SYNONYM [dbo].[Alumni] FOR [dbo].[OldStudents2]
SELECT * FROM [dbo].[Alumni]
This work around for synonym chaining will only work if the base object used in the synonym is either a table or a view.