SQL如何分組行正確

Question

我有三個表：

**Bookie**: 

------------ 

Id : int (Primary Key) 

Bookie : varchar 

---

**Transactions**: 

------------------- 

Id : int (Primary Key) 

Date : date 

Bookie : int (Foreign Key) 

Amount : decimal 

---

Wagers: 

Id : int (Primary Key) 

Stake : decimal 

Bookie : int (Foreign Key) 

下注表不是全部，但對於SQL這些列就足夠了。

我想這SQL代碼至今：

SELECT Bookie.Bookie, SUM(Amount), Wagers.Stake FROM Transactions 
JOIN Bookie on Transactions.Bookie = Bookie.Id 
JOIN Wagers on Bookie.Id = Wagers.Bookie 
GROUP BY Bookie.Bookie, Wagers.Stake 

但我的輸出是這樣的：

Bookie | Amount | Stake 
William Hill | 600.00 | 14.70 
Bet at Home | 500.00 | 30.00 
Bet at Home | 500.00 | 45.00 
Bet at Home | 500.00 | 50.00 
Bet365 | 10200.00 | 100.00 

它應該是這樣的：

Bookie | Amount | Stake 
William Hill | 600.00 | 14.70 
Bet at Home | 500.00 | 125.00 
Bet365 | 10200.00 | 100.00 

有誰知道要實現這個問題？

感謝

Answer 1

您需要聚合Stake：

SELECT Bookie.Bookie, SUM(Amount) AS Amount, SUM(Wagers.Stake) AS Stake 
FROM Transactions 
JOIN Bookie 
    ON Transactions.Bookie = Bookie.Id 
JOIN Wagers 
    ON Bookie.Id = Wagers.Bookie 
GROUP BY Bookie.Bookie; 

編輯：

SELECT Bookie, MAX(Amount) AS Amount, SUM(Stake) AS Stake 
FROM (
    SELECT Bookie.Bookie, SUM(Amount) AS Amount, Wagers.Stake 
    FROM Transactions 
    JOIN Bookie on Transactions.Bookie = Bookie.Id 
    JOIN Wagers on Bookie.Id = Wagers.Bookie 
    GROUP BY Bookie.Bookie, Wagers.Stake 
) AS sub 
GROUP BY Bookie; 

Answer 2

來自兩個不同的表集料最好是預彙總的數據，只然後加入：

select 
    b.bookie, 
    t.sum_amount, 
    w.sum_stake 
from bookie b 
join 
(
    select bookie, sum(amount) as sum_amount 
    from transactions 
    group by bookie 
) t on t.bookie = b.id 
join  
(
    select bookie, sum(stake) as sum_stake 
    from wagers 
    group by bookie 
) w on w.bookie = b.id; 

由於您只關心每個表中的一個聚合，您甚至可以在select子句中使用相關子查詢。易寫易讀:-)

select 
    b.bookie, 
    (select sum(t.amount) from transactions t where t.bookie = b.id), 
    (select sum(w.stake) from wagers w where w.bookie = b.id) 
from bookie b