[sql] Using SELECT result in another SELECT

What you are looking for is a query with WITH clause, if your dbms supports it. Then

WITH NewScores AS (
    SELECT * 
    FROM Score  
    WHERE InsertedDate >= DATEADD(mm, -3, GETDATE())
)
SELECT 
<and the rest of your query>
;

Note that there is no ; in the first half. HTH.