Transform a table column into a CSV field in SQL Server

Imagine that you want to use a related table in your SQL query. You then must return only a single column or otherwise you'll get this SQL error:Msg 512, Level 16, State 1, Line 2Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.What I like to do, is to transform the result table column into a