mysql tips - JOIN and GROUP BY - complex query example
SELECT td.c1, td.c2, sum(tc.c3) FROM (SELECT tc.*, tb.c1, tb.c2 FROM tb JOIN (SELECT ta.c1, ta.c2, sum(ta.c3) FROM ta WHERE... GROUP BY...) tc ON tb.c4=ta.c5) td GROUP BY td.c1, td.c2