GROUP BY 並為分組的每個唯一值創建列（始終輸出為 1 行），然后使用 output 作為 JOIN - SQL 服務器

Question

我需要按 2 列（BillingId 和 PaymentType）對數據進行分組——這沒有問題，並且有 1 行的 output 和唯一的 PaymentType 列——這一步有問題。 所以每個 BillingId 只有 1 行，該表將用於連接數據庫中的另一個表。

計費表：

BillingId (unique)

 12345
 67890

付款表：

PaymentId PaymentType  BillingId PaymentAmount
 (unique)

   12      electronic    12345      62.29
   14      electronic    12345      73.28
   56      electronic    12345     -62.29
   6       electronic    67890      83.58
   2       adjustment    67890      30.43

我的代碼：

SELECT GroupedTable.* 

FROM (SELECT b.BillingId, 
             p.PaymentType, 
             SUM(p.PaymentAmount) AS AmountPaid
      FROM Billing AS b
      LEFT JOIN Payment AS p
        ON (b.BillingId = p.BillingId)
      GROUP BY b.BillingId, p.PaymentType) AS GroupedTable

OUTPUT（顯然不正確）：

  BillingId  PaymentType   AmountPaid

     67890    electronic    83.58
     12345    electronic    73.28
     67890    adjustment    30.43

OUTPUT 我需要：

BillingId    AmountPaid     AmountAdjusted 
            (electronic)     (adjustment)

  67890         83.58           30.43
  12345         73.28            0

Answer 1

如果使用Case When表達式，看起來會更容易，如下所示：

Select B.BillingId, Sum(Case When P.PaymentType='electronic' Then P.PaymentAmount End) As [AmountPaid (electronic)],
                    Sum(Case When P.PaymentType='adjustment' Then P.PaymentAmount End) As [AmountAdjusted (adjustment)] 
From Billing As B Left Join Payment As P On (B.BillingId=P.BillingId)
Group by B.BillingId

db<>小提琴

帳單編號	支付金額（電子版）	AmountAdjusted（調整）
12345	73,28	NULL
67890	83,58	30,43

Answer 2

您應該僅按BillingId分組並使用條件聚合：

SELECT b.BillingId, 
       SUM(CASE WHEN p.PaymentType = 'electronic' THEN p.PaymentAmount ELSE 0 END) AS AmountPaid,
       SUM(CASE WHEN p.PaymentType = 'adjustment' THEN p.PaymentAmount ELSE 0 END) AS AmountAdjusted
FROM Billing AS b LEFT JOIN Payment AS p
ON b.BillingId = p.BillingId
GROUP BY b.BillingId;

請參閱演示。