Question

我想从mysql中选择数据。并且还希望在查询执行时进行一些计算。我有两个sql表：

贷款表：

loan_id|Customer_name|Total_amount
1000   |Sashika      |55000
1001   |Amell        |11000

结算表：

Sett_id|Loan_id|Amount
a123    |1000    |1000
b123    |1001    |2000

这就是我的两张桌子的样子。我想获得贷款的应有价值。我使用下面的代码生成，但它不会显示正确的值。

select loan.loan_id,loan.customer_name,loan.total_amount,sum(settlement.amount) as 'Total Received',
      ((loan.total_amount)-sum(settlement.amount ))as 'Total Due'
from loan , settlement
where loan.loan_id = 1001;

此代码获取settelement表的total（列）值。当我尝试使用另一个贷款ID（其中loan_id =）时，还显示和计算结算价值总额。但这不是我想要的价值。请帮帮我们

Loan_ID| Customer_Name|Total_Amount|Total_Received|Total_Due
1000       |Sashika       |55000       |1000          |54000

这就是我想要的 感谢您编辑我的问题并使其更易理解：）

Answer 1

您应该使用内部联接和分组

select 
    loan.loan_id
   ,loan.customer_name
   ,loan.total_amount
   ,sum(settlement.amount) as 'Total Received'
   ,((loan.total_amount)-sum(settlement.amount ))as 'Total Due' 
from loan 
inner join settlement  on  loan.loan_id =  settlement.loan_id
where loan.loan_id=1001
group by load.loan_id

Answer 2

我会推荐这样的查询：

select l.*, (l.total_amount - s.amount) as amountDue
from loans l left join
     (select loan_id, sum(amount) as amount
      from settlement s
      group by loan_id
     ) s
     on l.loan_id = s.loan_id;

您的查询存在许多问题：

您正在使用聚合函数，但没有group by。
select。
您使用的是join语法的古老形式。简单规则：从不在from子句中使用逗号。

我还建议您不要对列别名使用单引号。 MySQL中正确的转义字符是反引号。仅对字符串和日期常量使用单引号。

Answer 3

尝试，如果ID 1001没有结算，则内部联接不起作用，它将显示0行，显示收到的总数为null我已经改变了内部到左边的连接

select loan.loan_id, loan.customer_name, loan.total_amount, 
sum(settlement.amount) as ''Total Received',
((loan.total_amount)-sum(settlement.amount )) as 'Total Due'
from load
left join settlement
on settlement.loan_id = loan.loan_id
where loan.loan_id = 1001;

Answer 4

这是我的版本：

select 
    loan.loan_id,
    loan.customer_name,
    loan.total_amount,
    ifnull(sum(settlement.amount), 0) as 'Total Received',
    ((loan.total_amount) - ifnull(sum(settlement.amount), 0)) as 'Total Due' 
from loan
left join settlement on
    settlement.loan_id = loan.loan_id
where 
    loan.loan_id=1000

您需要一个LEFT JOIN，而不是内部联接来处理尚未付款的情况。如果sum(settlement.amount)表中没有条目，您还需要确保NULL不返回settlement，否则'总截止日期'也将是NULL。

如果你一次只承担一次负担，你实际上并不需要像GROUP BY这样的人。

选择＆amp;计算SQL但回答错误

4 个答案: