MySQL多表联合统计查询问题

创建表，数据

create table a

(id int,

项目号 varchar(2),

总金额 int,

上家单位 varchar(4))

insert into a values (1,'01',100,'AAAA')

insert into a values (2,'02',200,'BBBB')

insert into a values (3,'03',250,'CCCC')

create table b

(id int,

项目号 varchar(2),

到款 int,

到款时间 date)

insert into b values (1,'03',50,'2018-07-23')

insert into b values (2,'03',100,'2018-07-24')

insert into b values (3,'01',80,'2018-07-25')

执行：

SELECT

a.项目号,

a.总金额,

sum(

CASE

WHEN a.项目号 = b.项目号 THEN

到款

ELSE

0

END

) 到款总额

FROM

a

LEFT JOIN b ON a.项目号 = b.项目号

GROUP BY

a.项目号,

a.总金额

结果：

SELECT m.user_id, b_total, c_total, d_total FROM a m, (SELECT user_id, COUNT(*) b_total FROM b GROUP BY user_id) n,

(SELECT user_id, COUNT(*) c_total FROM c GROUP BY user_id) j, (SELECT user_id, COUNT(*) d_total FROM d GROUP BY user_id) k,

WHERE m.user_id = n.user_id AND m.user_id = j.user_id AND m.user_id = k.user_id

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