How SQL Server synonyms help database DevOps

Synonyms inside SQL Server are one of those useful but forgotten features. A synonym is a database level object that allows you to provide an alternative name for another database object such as a view, user defined table, scalar function, stored procedure, inline table valued function (tvf), or extended stored procedure. They can also be used for CLR Assembly related stored procedures, CLR tvf, CLR scalar functions or even CLR aggregate functions. There are many practical uses for synonyms, and I’ll explain how to create them and some use cases.

You can create a synonym using the GUI in SSMS or via a script. Here’s a sample script:

USE [AdventureWorks2014]
GO
CREATE SYNONYM [dbo].[EmployeeDemo] 
FOR [MRSurfacePro].[AdventureWorks2014].[HumanResources].[Employee]
GO

The example creates an alternate name for the HumanResources.Employee table. Note that creating the synonym requires a four-part name, including the server. Here’s an example of how to use the new synonym:

SELECT * from dbo.[EmployeeDemo]

If you also query the original table, you’ll see that it returns the same rows. You can reference the new name in code, linked servers, applications, and more. In situations where you would need to use a three- or four-part name, you can just use the synonym without having to use the multipart naming which greatly reduces the need for code changes.

There are a few caveats to this to keep in mind. Synonyms cannot be referenced things like CHECK constraints, computed columns, default expressions, rules expressions, schema bound views or functions. They also cannot be used in DDL (Data Definition Language) statements, to make changes to the underlying schema the synonym represents, you must reference the actual object name within any DDL statement.

We all know when developing objects, the naming that was used at the beginning of a project can change and get better over time. Using synonyms can be a real project time saver. You can continue to be agile and not have a huge need to back port changes. Synonyms can also help with database migrations from one server to another. How many times have you had to migrate to a server with a new name? This simplifies the process. All you would have to do is change the synonym definition four-part name; no other changes would be required.

Imagine how easy this can make DevOps. Say you have a cross-database view and database names are different on the development server or servers in the pipeline. If you use synonyms, no additional code changes are needed when referencing the view, and a post-deployment script could just change the synonym definition depending on the environment.

Synonyms simplify and remove the need for code changes. It’s definitely something to consider. I am always cautious as a DBA to recommend things like this as it tends to make it more difficult to track down issues and troubleshoot back to the original table or source, so be sure to document them. There are times, however, in which we need to accomplish things as I explained above, and synonyms are a great avenue to do so.

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