Question

我有这张表register

id quantity type
 1 |     10 | in
 2 |       5 | in
 1 |       3 | out
 1 |       2 | out
 2 |       5 | out
 3 |       2 | in
 3 |       1 | out

我想要每个股票的余额[类型的总和=＆＃39;在＆＃39; - 类型的总和=＆＃39; out＆＃39; ]
期望的输出将是

1 | 5
2 | 0
3 | 1

我还有另一张表item

id | name
1  | A
2  | B
3  | C

是否可以使用项目名称而不是ID来查看输出？所以最终结果就像

A | 5
B | 0
C | 1

Answer 1

基本思想是case内的条件聚合 - sum()。您还需要join才能获得name：

select i.name,
       sum(case when r.type = 'in' then quantity
                when r.type = 'out' then - quantity
                else 0
            end) as balance
from register r join
     item i
     on r.id = i.id
group by i.name;

Answer 2

根据上述问题中提到的描述，作为解决方案，请尝试执行以下SQL查询

SELECT i.name,
    @in_total:= (select sum(quantity) from register where type = 'in'
        and id = r.id group by id),
    @out_total:= (select sum(quantity) from register where type = 'out'
        and id = r.id group by id),
    @balance:= (@in_total - @out_total) as balance
FROM `register`
as r join item i on r.id = i.id group by r.id 
CROSS JOIN (SELECT @in_total := 0, 
                   @out_total := 0, 
                   @balance := 0) AS user_init_vars

MySql查询查找具有条件的相同列之间的差异

2 个答案: