Select TOP 1000 + custom user id's

Question

I want to select top 1000 user id's based on revenue in addition to a custom list of user id's (these are not part of the top 1000)

In other words, I want the queries below in 1 query:

SELECT TOP 1000 * FROM XX
ORDER BY REVENUE DESC

SELECT * FROM XX
WHERE USER_ID IN (CUSTOM_LIST)

Answer 1

You need a Union, but as TOP is not allowed in a Set-Select you must nest it in a Derived Table:

SELECT *
FROM
 (
   SELECT TOP 1000 * FROM XX
   ORDER BY REVENUE DESC
 ) as dt

 UNION
  -- UNION ALL is more efficient, but a user from the custom list who is 
  -- also in the top 1000 would be returned twice

SELECT * FROM XX
WHERE USER_ID IN (CUSTOM_LIST)