MySql从同一张表中查询贷方和借方

Question

我有一个 MySql 表来控制借方和贷方。它看起来像这样

id | status | type  | amount | value | expiration | parent_id | company_id |
---|--------|------ |--------|-------|------------|-----------|------------|
1  |    1   |credit | 46     | 42.00 | 2018-04-01 | 0         | 1          |
2  |    1   |credit | 33     | 194.00| 2017-07-07 | 0         | 1          |
3  |    1   |credit | 49     | 17.00 | 2016-11-11 | 0         | 1          |
4  |    1   |debit  | 1      | NULL  | NULL       | 1         | 1          |
5  |    1   |debit  | 1      | NULL  | NULL       | 1         | 1          |
6  |    1   |debit  | 1      | NULL  | NULL       | 2         | 1          |
7  |    1   |debit  | 1      | NULL  | NULL       | 2         | 1          |
8  |    1   |debit  | 1      | NULL  | NULL       | 2         | 1          |
9  |    1   |debit  | 1      | NULL  | NULL       | 2         | 1          |
10 |    1   |debit  | 1      | NULL  | NULL       | 3         | 1          |

我想检索一个人现在有多少学分。

将所有状态 = 1 的借方与状态 = 1 且到期的每个父贷方相加 > NOW()

然后从它的父信用中减去

在这种情况下，我应该得到类似的东西

总积分 = (46 - 2) + (33 - 4)

到目前为止我得到的是

SELECT SUM(amount) as tot_debit 
FROM credits
WHERE company_id = 1 
      AND status = 1 
      AND type = 'debit' 
      AND parent_id IN (SELECT id
                         FROM credits 
                         WHERE company_id = 1 
                           AND status = 1 
                           AND expiration > NOW() 
                           AND type = 'credit') 
GROUP BY parent_id

关于如何让它发挥作用的任何想法？

谢谢

Answer 1

您可以使用 correlation 来获得预期的结果：

SELECT SUM(amount) 
       -
       COALESCE((SELECT SUM(amount)
                 FROM credits AS c2
                 WHERE company_id = 1 AND status = 1 AND 
                       type = 'debit' AND
                       c2.parent_id = c1.id), 0)
FROM credits AS c1
WHERE company_id = 1 AND status = 1 AND 
      type = 'credit' AND expiration > NOW();

Demo here

Answer 2

您应该使用自左连接，以便每条记录都与其父记录匹配（如果存在）并过滤掉过期记录。然后使用有条件的总和，您可以添加贷方并减去借方。

SELECT  SUM(CASE WHEN type = 'credit' THEN amount ELSE amount * -1 END) AS total
FROM    credits t1
LEFT JOIN
        credits t2
ON      t1.parent_id = t2.id AND
        t2.expiration > NOW()
WHERE   t1.company_id = 1 AND 
        t1.status = 1 AND
        t1.expiration > NOW()

Answer 3

由于您在一张表中同时拥有贷方和借方（我不会推荐这种设计），因此这里最快的方法可能是聚合：

select sum(total)
from
(
  select 
    sum(case when type = 'credit' then value else -value end) as total
  from mytable
  where company_id = 1
  and status = 1
  group by case when type = 'credit' then id else parent_id end -- group by credit ID
  having sum(type = 'credit' and expiration > now()) > 0
) total_per_credit;

HAVING 子句在 MySQL 中使用 true = 1 / false = 0。 （在其他 DBMS 中，您将使用 CASE 构造。）