How to Write a Common Table Expression in SQL Server
Common table expressions (CTEs) are a great way to break up complex queries. SQL Server has supported this from the early beginning, starting with the 2005 version. Here's a simple query to illustrate how to write a CTE:
with free_users as ( select * from users where plan = 'free' ) select user_sessions.* from user_sessions inner join free_users on free_users.id = user_sessions.user_id order by free_users.id;
You can find more complex examples of using CTE's in How to Avoid Gaps in Data in SQL Server and in Calculating Cumulative Sums in SQL Server.