在动态变化的列上加入 2 个表

Question

拥有这 2 个表格（来自库存功能）

SQL Fiddle

-- ins table
+------+-------------+-------------+
| id   |  direction  |   quantity  |
+------+-------------+-------------+
|  1   |     in      |      5      |
|  2   |     in      |      3      |
+------+-------------+-------------+


-- outs table
+------+-------------+-------------+
| id   |  direction  |   quantity  |
+------+-------------+-------------+
|  1   |     out     |      4      |
|  2   |     out     |      1      |
|  3   |     out     |      2      |
|  4   |     out     |      1      |
+------+-------------+-------------+

如何将 outs 表中的行连接到 ins 表中数量覆盖/等于加入它的 outs 行的数量的行，换句话说 如何获得这样的结果？

-- result
+------+-------------+-------------+------+-------------+-------------+
| id   |  direction  |   quantity  |  id  |  direction  | quantity    |
+------+-------------+-------------+------+-------------+-------------+
|  1   |     out     |      4      |  1   |     in      |      5      |
|  2   |     out     |      1      |  1   |     in      |      5      |
|  3   |     out     |      2      |  2   |     in      |      3      |
|  4   |     out     |      1      |  2   |     in      |      3      |
+------+-------------+-------------+------+-------------+-------------+

如您所见，outs 表的第 1,2 行取自/连接到ins 表的第 1 行，outs 表的第 3,4 行取自/连接到 @987654331 的第 2 行@表

注意：保证 2 个表中的数量是密封的（ins 表中的一行始终具有完全等于表 @987654333 中的 1 个或多个行的数量@)

我希望我能做这样的事情

-- sedu SQL
SELECT 
    whatever 
FROM 
    outs left join 
    ins on outs.quantity <= (ins.quantity - previously joined outs.quantities);

Answer 1

由于几个原因，在 MySQL 中这样做很痛苦。首先，MySQL 对累积和的支持不是很好，这是您要比较的。

其次，您的结果集有点弱。显示所有对每个outs 记录有贡献的ins 记录更有意义，而不仅仅是其中一个。

为此，您可以对累积和使用连接，如下所示：

select o.*, (o.to_quantity  - o.quantity) as from_quantity,
       i.*
from (select o.*,
             (select sum(o2.quantity)
              from outs o2
              where o2.id <= o.id
             ) as to_quantity
      from outs o
     ) o join
     (select i.*,
             (select sum(i2.quantity)
              from ins i2
              where i2.id <= i.id
             ) as to_quantity
      from ins i
     ) i
     on (o.to_quantity  - o.quantity) < i.to_quantity and
        o.to_quantity > (i.to_quantity  - i.quantity)

Here 是 SQL Fiddle。

Answer 2

子查询与相关方法也可能有用

select t.id, t.direction, t.quantity, i.id, i.direction, i.quantity  
from (
      select id, direction, quantity, 
             quantity + coalesce((select quantity from outs where id < o.id order by id desc limit 1),
                      (select quantity from outs where id > o.id order by id limit 1)) Qty
      from outs o
)t inner join ins i on i.quantity = t.Qty