khz0912 a,khz1001 b两张表，字段一样，按照表A的客户号统计，一个客户号对应多个数据纪律，月初余额 ycye，月末余额 ymye，sql怎么写？
------解决方案--------------------------------------------------------
select a,b,sum(c) from
(
select a,b,c from A表
union all
select a,b,-c from B表
) t
group by a,b
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select a,b,sum(c) from
(
select a,b,c from A表
union all
select a,b,-1*c from B表
) aa group by a,b
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select A表.a,A表.b,A表.c-B表.c
from A表 left join B表 on A表.a=B表.a
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SELECT X.a, X.b, (X.t - Y.t) t
FROM
(
SELECT A.a, A.b, SUM(A.c) t
FROM A
GROUP BY A.a, A.b
) X LEFT JOIN
(
SELECT B.a, B.b, SUM(B.c) t
FROM B
GROUP BY B.a, B.b
) Y ON (X.a = Y.a AND X.b = Y.b)
------解决方案--------------------------------------------------------