SQL Server：在結果集中查找最大值

Question

我有這段代碼，我很難理解它爲什麼不起作用。我已經搜索瞭解決方案，這實際上是我的代碼結束了它的方式，但它只是不正確的工作......任何幫助將不勝感激。

我想要做的是爲每個客戶端選擇一條記錄。所選的記錄應該是債務人餘額最高的記錄。相反，我將所有債務人的餘額全部拿到手。幾乎像它不是將它們分組返回給客戶端...

SELECT 
    Debtorness.ClientName, 
    Debtorness.DebtorName, 
    MAX(Debtorness.DFB) 
FROM 
    (SELECT 
     Clients.Name AS ClientName, 
     Debtors.Name AS DebtorName, 
     (CalcAging.FundedBalance) AS DFB 
    FROM 
     Clients 
    INNER JOIN 
     CalcAging ON Clients.ClientKey = CalcAging.ClientKey 
    INNER JOIN 
     Debtors ON CalcAging.DebtorKey = Debtors.DebtorKey 
    INNER JOIN 
     CalcClient ON Clients.ClientKey = CalcClient.ClientKey 
    WHERE 
     Clients.Inactive='0' 
    GROUP BY 
     Clients.Name, Debtors.Name, CalcAging.FundedBalance, 
     CalcAging.MasterDebtorKey) AS Debtorness 
GROUP BY 
    Debtorness.ClientName, Debtorness.DebtorName, Debtorness.DFB 
ORDER BY 
    Debtorness.ClientName ASC 

是我所得到的示例輸出：

Client1 | Debtor23 | Balance  
Client1 | Debtor47 | Balance 
Client1 | Debtor14 | Balance 
Client2 | Debtor72 | Balance 
Client2 | Debtor30 | Balance 

等等......對於所有的客戶。再次，我想看到所有的客戶，但我只想要那個客戶的餘額最高的債務人......謝謝！

Answer 1

使用row_number()

WITH cte as (
    SELECT 
     Clients.Name AS ClientName, 
     Debtors.Name AS DebtorName, 
     CalcAging.FundedBalance AS DFB, 
     ROW_NUMBER() over 
      (PARTITION BY Clients.Name ORDER BY CalcAging.FundedBalance DESC) as rn 
    FROM  
     Clients INNER JOIN 
     CalcAging ON Clients.ClientKey = CalcAging.ClientKey INNER JOIN 
     Debtors ON CalcAging.DebtorKey = Debtors.DebtorKey INNER JOIN 
     CalcClient ON Clients.ClientKey = CalcClient.ClientKey 
    WHERE 
     Clients.Inactive='0' 
) 
SELECT * 
FROM cte 
WHERE rn = 1; 

Answer 2

一個快速和骯髒的解決辦法是做一個選擇在你當前的結果。這是要繼續工作用你已經有和你已經知道如何使用。

的結果：

select clientname,debtorname,balance_column from (SELECT Debtorness.ClientName, 
    Debtorness.DebtorName, 
    MAX(Debtorness.DFB) 
FROM (

SELECT 
    Clients.Name AS ClientName, 
    Debtors.Name AS DebtorName, 
    (CalcAging.FundedBalance) AS DFB 
FROM  
    Clients INNER JOIN 
    CalcAging ON Clients.ClientKey = CalcAging.ClientKey INNER JOIN 
    Debtors ON CalcAging.DebtorKey = Debtors.DebtorKey INNER JOIN 
    CalcClient ON Clients.ClientKey = CalcClient.ClientKey 
WHERE 
    Clients.Inactive='0' 
GROUP BY 
    Clients.Name, Debtors.Name, CalcAging.FundedBalance, CalcAging.MasterDebtorKey 
) AS Debtorness 
GROUP BY Debtorness.ClientName, Debtorness.DebtorName, Debtorness.DFB 
ORDER BY Debtorness.ClientName Asc) group by clientname having a.balance_column = Max(a.balance_column)