MySQL数据库中如何解决分组统计的问题

--------------------------------       A　     |　B　 |　C　  |　D       a   b   |   a   c   |   a   d   |   d   e       1   1   |   1   1   |   1   A   |   A   1       2   2   |   1   3   |   2   B   |   B   2       3   4   |   1   4   |   3   C   |   C   3       4   6   |   2   1   |   4   D   |   D   4       --------------------------------

1   1   3   1       2   2   1   2       3   4   0   3       4   6   0   4

select A.a,A.b,IFNULL(c,0) as c,D.a from (select 1 as a,2 as b union allselect 2 as a,2 as b union allselect 3 as a,4 as b union allselect 4 as a,6 as b) as A left outer join     (select a,count(a) as c from(select 1 as a,3 as c union allselect 1 as a,3 as c union allselect 1 as a,3 as c union allselect 2 as a,3 as c ) B group by a) as Bon A.a=B.a join (select 1 as a,'A' as d union allselect 2 as a,'B' as d union allselect 3 as a,'C' as d union allselect 4 as a,'D' as d ) as C on A.a=C.a join(select 1 as a,'A' as d union allselect 2 as a,'B' as d union allselect 3 as a,'C' as d union allselect 4 as a,'D' as d ) as Don D.d=C.d