SELECT *
    Main.*,
    Sub1.*,
    Sub2.*,
    ...
FROM Main
LEFT JOIN (
    SELECT T1.main_id, SUM(T1.col1) as stat1, AVG(T2.col2) as stat2
    FROM T1
    GROUP T1.main_id
) Sub1 ON Sub1.main_id = Main.id
LEFT JOIN (
    SELECT T2.main_id, COUNT|AVG|SUM
    FROM T2
    GROUP T2.main_id
) Sub2 ON Sub2.main_id = Main.id
LEFT JOIN ( T3 ... )