MYSQL：如何从三个表返回查询计算结果？

Question

I have three tables:

Table1: Salary
Fields: ID,Account_Num,Amount

Table2: Other_Income
Fields: ID,Account_Num,Amount

Table3: Expenses
Fields: ID,Account_Num,Amount

From the above tables,how to write a query which return a result, list all account from these table, and shows the balance of every account in these tables.

Result should show Account_num,Salary,Other_Income,Expenses, balance ( balance=Salary.amount+Other_Income.amount-expenses.amount )

These three table may contains some different account number.

I have been thinking of this so long, tried union and join but still cant make it.

Somebody show/guide me?

Answer 1

I've had some luck with the following query. Essentially, I combine all the transactions in the Salary, Other_Income and Expenses tables into a single temp table named combined, and then use group by to sum all the transactions!

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

Following query might help , provided that every account has salary against it.

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。