MYSQL：如何从三个表返回查询计算结果？

Question

我有三个表：

Table1: Salary
Fields: ID,Account_Num,Amount

Table2: Other_Income
Fields: ID,Account_Num,Amount

Table3: Expenses
Fields: ID,Account_Num,Amount

从上面的表格中，如何编写查询以返回结果，列出这些表格中的所有帐户，并显示这些表格中每个帐户的余额。

结果应显示Account_num,Salary,Other_Income,Expenses, balance （ balance=Salary.amount+Other_Income.amount-expenses.amount ）

这三个表可能包含一些不同的帐号。

我一直在想这个很久了，尝试过加入并加入，但仍然做不到。

有人向我展示/引导我吗？

Answer 1

我对以下查询有好运。 本质上，我将Salary，Other_Income和Expenses表中的所有交易合并到一个名为Combine的临时表中，然后使用group by汇总所有交易！

select Account_Num, sum(Amount)
from (
  select Account_Num, Amount from Salary union
  select Account_Num, Amount from Other_Income union
  select Account_Num, -Amount from Expenses
) as Combined
group by Account_Num;

Answer 2

如果每个帐户都有薪水，以下查询可能会有所帮助。

select  Account_Num,(total-d.Amount) as final_amount ( select Account_Num, ifnull(a.Amount,0)+ifnull(b.Amount,0) as total from Salary a
   left join Other_Income b on a.Account_Num=b.Account_Num ) c
   join Expenses d on c.Account_Num=d.Account_Num 

Answer 3

    SELECT Sal.`Account_Num`, sal.`Amount` AS Salary, ot_in.`Amount` AS ExtraIncome , exp.`Amount` AS expenses, (sal.`Amount`+ot_in.`Amount`-exp.`Amount`) As Balance FROM Salary AS Sal INNER JOIN Other_income AS ot_in ON Sal.`Account_Num` = ot_in.`Acount_num` INNER JOIN Expenses AS exp ON Sal.`Account_Num` = ex.`Account_Num`   

在这里，您要从这三个表中获得通用帐号并从每个表中提取对应的金额，然后将表中的三个表连接起来，并使用给定的公式从收入中减去支出来计算剩余余额。我希望这会有所帮助。