MySQL从多个表中选择和求和，不重复

我有三张桌子：

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

=======

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

=======

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

在那个查询中，我得到的结果是这样的……代码B001输出46和输入18，代码B002输出80和输入30，代码B003输出null和输入null

如何解决此问题？

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

---

使用一个子查询、

UNION

子句和

GROUP

ping，我构建了以下查询：

SELECT
  p.code,
  p.name,
  -- Using IFNULL to handle products without stock variation
  IFNULL(SUM(q.q_in), 0) AS total_in,
  IFNULL(SUM(q.q_out), 0) AS total_out,
  -- Compute the new stock level
  p.qty + IFNULL(SUM(q.q_in), 0) - IFNULL(SUM(q.q_out), 0) AS qty
FROM (
  -- UNION (= concatenate) prod_in and prod_out tables
  SELECT
    product,
    qty AS q_in,
    0 AS q_out    -- Enforce schema (otherwise, q_out is dropped)
  FROM prod_in 
  UNION
  SELECT
    product,
    0 AS q_in,
    qty AS q_out
  FROM prod_out
) AS q
-- Using a RIGHT join to show products without stock variations
RIGHT JOIN products AS p
  ON p.code = q.product
-- Group by id to get the summarized view
GROUP BY q.product

---

这里是一个带有示例数据的查询

Use

left-outer-join

，您将得到B003的结果。对于其他错误结果，请尝试从中选择*。。。查看查询的结果。