Displaying Statement Completion (SQL-editor, Visual Studio 2015)

Hi all.

I am trying to learn about VSIX and code completion. I'm wondering about the SQL Editor in visual studio 2015, it is not detected by the ICompletionSourceProvider. I am using the MSDN Walkthrough as test case.

https://msdn.microsoft.com/en-us/library/ee372314.aspx

The code completion appears when im using a regular .txt or .cs file, how do I get the .sql files to work?
Documentation about using SQL in visual studio seems scarse when it comes to the extention SDK.

I would appreciate any input.