MySQL从隔离子查询中减去 [英] MySQL subtract from isolated subquery

问题描述

我有一个包含库存的表

ID   |   Product ID   |  In_Transit  |   Quantity   | Cumulative Quantity
=====+================+==============+==============+====================
1    |      1         |     0        |     1000     |      1000
2    |      1         |     0        |        1     |      1001
3    |      1         |     1        |       54     |      1055
4    |      1         |     1        |        1     |      1056

因此，产品ID为1的总库存为'1056'，我可以通过使用SELECT MAX(ID)子查询与表进行连接来获得其累计数量为1056.

So the total inventory for product id 1 is '1056' I get this using a SELECT MAX(ID) subquery join with the table to get its cumulative quantity which is 1056.

我想获取库存总额(减去运输中的所有金额)

I would like to get the Inventory total (subtracting all the amounts in transit)

所以1056-54-1 = 1001

So 1056 - 54 - 1 = 1001

如何在一个查询中得到它，所以我得到

How would I get this in one query so i get

Product ID | Total Inventory | Inventory on Hand (Excluding in Transit |
===========+=================+=========================================    
1          |     1056        |           1001

我还需要使用累积清单来获取总计，而不是"SUM"，除了对运输中的那些求和，因为(那些未在运输中的)拥有大量记录，并且需要一些时间才能达到SUM.我可以用它来汇总运输中的记录，因为记录要少得多

Also i need to use the cumulative inventory to get the total as opposed to 'SUM', except for summing those in transit because (those not in transit) have a large number of records and they take ages to SUM. I can use it to sum those in transit because there are far fewer records

推荐答案

SELECT 
    a.product_id
  , a.cumulative as total_inventory
  , a.cumulative - COALESCE(b.quantity,0) AS inventory_on_hand
FROM table1 a
JOIN 
    ( SELECT MAX(id) AS max_id
      FROM table1
      GROUP BY product_id
    ) m ON (m.max_id = a.id)
LEFT JOIN
    ( SELECT product_id, SUM(quantity) 
      FROM table1 
      WHERE in_transit = 1
      GROUP BY product_id
    ) b ON (a.product_id = b.product_id)

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