MySQL从多个表中进行选择和求和而不重复

Question

我有 3 张 table :

table1

code(Primary key) | name | quantity

B001 | sand | 50

B002 | nail | 100

B003 | paint | 10

=======

table2

code | qty_out

B001 | 2

B001 | 1

B001 | 20

B002 | 10

B002 | 30

=======

table3

code  | qty_in

B001   | 1

B001   | 5

B002   | 5

B002  | 10

=======

我想要的结果是:

table1

code  | name    | quantity  | Out      | In      | total

B001  | sand    | 50        | 23       | 6       | 33

B002  | nail    | 100       | 40       | 15     |  75

B003  | paint   | 10        | null/0  |  null/0  | 10

我使用了这个查询:

SELECT table1.code, table1.name, table1.quantity, sum(table2.qty_out ) AS 'Out', sum( table3.qty_in ) AS 'In'
FROM table1
LEFT JOIN table2 ON table2.code = table1.code
LEFT JOIN table3 ON table3.code = table1.code
GROUP BY table1.code
ORDER BY table1.code ASC

在该查询中，我得到这样的结果...code B001 out 46 and in 18, code B002 out 80 and in 30, code B003 out null and in null

如何解决这个问题？

Answer 1

使用此查询

select t.code,t.name,t.quantity,t.out,t.in,(t.out+t.in) as total
from ( 
      SELECT table1.code, table1.name, table1.quantity,
                ( select sum(table2.qty_out) 
                  from table2 
                  where table1.code=table2.code ) as out,
                ( select sum(table3.qty_in) 
                  from table3
                  where table3.code=table1.code ) as in  
      FROM table1
     ) as t