mysql - MySQL查询根据另一个值将列视为正数或负数

Question

我在 MySQL 中有一个表，其结构如下：

table1
------
userid  varchar(20)
type    varchar(20)
amount  integer

类型可以是deposit或withdrawal。

我想在这个表上执行一个查询，在这里我可以获得取款总和的净余额 - 给定用户的存款。

这对 MySQL 是否可行，还是我需要运行两个单独的查询并在代码中进行减法？

Answer 1

这个怎么样：

select sum(
          case type
          when 'deposit' then amount
          when 'withdrawal' then -amount
          end 
          ) as balance
from $table where userid = $id

Answer 2

你可以执行这样的事情。调整表名和您的类型值。它将对每个用户的总存款和借记进行分组，并为您提供一个余额列。

SELECT userid, 
   Sum(CASE 
         WHEN [type] = 'Deposit' THEN amount 
         ELSE 0 
       END) AS deposit, 
   Sum(CASE 
         WHEN [type] = 'Debit' THEN amount 
         ELSE 0 
       END) AS debit, 
   Sum(CASE 
         WHEN [type] = 'Deposit' THEN amount 
         ELSE amount * -1 
       END) AS Balance 
   FROM   tblaccount 
GROUP  BY userid 

Answer 3

子查询应该能够做到这一点：

select 
   (select sum(amount) 
    from table1 
    where type='deposit' 
    and userid = 'user1'
   ) - 
   (select sum(amount) 
    from table1 
    where type='withdrawal' 
    and userid = 'user1') 
 as deposit_minus_withdrawls

或带有案例陈述。

SELECT userid, SUM( 
  CASE TYPE WHEN  'withdrawal'
  THEN amount
  ELSE 0 
  END ) - 
  SUM( 
  CASE TYPE WHEN  'deposit'
  THEN amount
  ELSE 0 
  END ) AS balance
FROM table1
GROUP BY userid
LIMIT 0 , 30