mysql - 我可以从同一列中选择值并将它们显示在2列结果中吗？

Question

假设我有一个帐户项移动表，就像

ACCOUNTS table 
+-------+------+---------+ 
| title | side | balance | 
+-------+------+---------+ 
| cash | debit| 500.0 | 
+-------+------+---------+ 
| cash |credit| 300.0 | 
+-------+------+---------+ 
| cash |credit| 600.0 | 
+-------+------+---------+ 
#..... more than 10'000 debit and credit rows 

我想组信用行之和借记行的总和，并显示在不同的列他们的每一笔。

什么，我试图做的是总结在两侧的群体的平衡，就像

select title, side, sum(balance) from accounts group by side 

我得到行，一个为借方金额，另一个是信贷总和，像

+-------+------+---------+ 
| cash | debit| 500.0 | 
+-------+------+---------+ 
| cash |credit| 900.0 | 
+-------+------+---------+ 

---

我想是获得整个导致一个结果行，德的总和一个字段中的位和另一个字段中的信用总和。我想最终的结果是这样的

+-------+-------+-------+ 
| cash | 500.0 | 900.0 | 
+-------+-------+-------+ 

谢谢。

Answer 1

您可以使用情况

select title, sum(case side when 'debit' then balance else 0 end), 
    sum(case side when 'credit' then balance else 0 end) 
from accounts 
group by title 

Answer 2

下面是使用子查询的一个例子。比已经提供的CASE语句冗长得多，但是如果你最终拥有多个标题或者想要进行计算，它就会变得非常简单。

SELECT 
    title 
    ,credit.credit_balance 
    ,debit.debit_balance 
    ,(credit.credit_balance - debit.debit_balance) AS net 
FROM 
    (SELECT 
     title, 
     sum(balance) debit_balance 
    FROM accounts 
    WHERE 
     side = 'debit' 
    GROUP BY side) debit 
INNER JOIN (
    SELECT 
     title, 
     sum(balance) debit_balance 
    FROM accounts 
    WHERE 
     side = 'credit' 
    GROUP BY side) credit ON debit.title = credit.title 
GROUP BY 
    title;