我有四张表A、B、C、D，
--------------------------------
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
--------------------------------
现在要用一条sql语句将A表所有的列，B表对与A表a字段
相关联的列求count,通过C表,将D表与A表关联起来，得到
结果
1 1 3 1
2 2 1 2
3 4 0 3
4 6 0 4
Mysql语句解决:
select
A.a,A.b,IFNULL(c,
0
)
as
c,D.a
from
(
select
1
as
a,
2
as
b
union
all
select
2
as
a,
2
as
b
union
all
select
3
as
a,
4
as
b
union
all
select
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
all
select
1
as
a,
3
as
c
union
all
select
1
as
a,
3
as
c
union
all
select
2
as
a,
3
as
c ) B
group
by
a)
as
B
on
A.a
=
B.a
join
(
select
1
as
a,
'
A
'
as
d
union
all
select
2
as
a,
'
B
'
as
d
union
all
select
3
as
a,
'
C
'
as
d
union
all
select
4
as
a,
'
D
'
as
d )
as
C
on
A.a
=
C.a
join
(
select
1
as
a,
'
A
'
as
d
union
all
select
2
as
a,
'
B
'
as
d
union
all
select
3
as
a,
'
C
'
as
d
union
all
select
4
as
a,
'
D
'
as
d )
as
D
on
D.d
=
C.d