sql server服務器結果的兩倍和三倍

Question

我想創建一個特定的表，但某些數值在結果中翻倍或翻倍。 這裏的情況是：

2表：付款和費用

[Payments]: ID, studentID, Amount, DOP (a row in this table is a payment which a student pays it on DOP (date). 
[Expenses]: ID, AmountPaid, TimeStamp (a row in this table is an expense bought such as papers or pens... on a specific date(timestamp) 

我的查詢是：

select 
sum(purchases.amount) as 'Income From Students', 
sum(Expenses.amountpaid) as 'Expenses', 
sum(purchases.amount-expenses.amountpaid) as 'Net Profit', 
datename(month,timestamp) as 'Month', 
datepart(year,timestamp) as 'Year' 
from expenses,purchases 
group by datename(month,timestamp),datepart(year,timestamp) 

爲查詢講述：我的表應該顯示每月和每年的付款總額，費用和淨額profit=payments - expenses。

問題是，當得到結果時，sum（expenses.amountpaid）總是加倍。

所以有什麼想法...

Answer 1

我解決了這傢伙，4個小時，試圖後，查詢是：

select sum(P.Income) as 'Income from Payments', 
sum(E.expense) as 'Expenses', 
sum(P.Income)-sum(E.expense) as 'Net Profit', 
DateName(month , DateAdd(month , IncomeMonth , 0) - 1) as 'Month' 
from 
(select sum(payments.amountpaid) as Income, 
month(DOP) as IncomeMonth 
from payments group by month(dop)) as P, 
(select sum(expenses.amountpaid) as Expense, 
month(timestamp) as ExpenseMonth 
from expenses 
group by month(timestamp)) 
as E 
where 
E.Expensemonth=P.IncomeMonth 
group by P.IncomeMonth 

Answer 2

聽起來像你需要指定兩個表之間的關係。

這樣的事情，我認爲：

select 
sum(purchases.amount) as 'Income From Students', 
sum(Expenses.amountpaid) as 'Expenses', 
sum(purchases.amount-expenses.amountpaid) as 'Net Profit', 
datename(month,timestamp) as 'Month', 
datepart(year,timestamp) as 'Year' 
from expenses,purchases 
WHERE PURCHASES.DOP = EXPENSES.TIMESTAMP /*Add this*/ 
group by datename(month,timestamp),datepart(year,timestamp) 

Answer 3

SELECT T.INCOME,T.EXPENSE,SUM(T.INCOME)-SUM(T.EXPENSE) AS PROFIT 
FROM (SELECT SUM(P.amount) AS Income, SUM(E.amountpaid) AS Expense 
FROM Payments P,Expenses E WHERE P.ID=E.ID 
GROUP BY datename(month, timestamp), datepart(year, timestamp)) AS T;