具有左聯接的SQL查詢聯合

Question

我有一個表（TableA），其中包含一些數據和TableB的外鍵

TableA
 --------------------
| ID  | Name  | FK   |
 --------------------
   0     A      1
   1     B      3
   2     C      1
   3     D      2
   4     E      4
  ...

TableB
 ----------------
| PK  | Status  | 
 ----------------
   1    A21   
   2    A22   
   3    A23   
   4    A24 

現在，我想計算TableA中有多少個條目具有TableB中的狀態...到目前為止沒有問題：

SELECT Count(TableA.FK) AS COUNTA, TableB.Status AS Status
    FROM TableB
LEFT JOIN TableA ON TableB.PK = TableA.FK
    GROUP BY TableB.Status, TableB.PK;

輸出：

 ------------------
| COUNTA  | Status | 
 ------------------
   2        A21   
   1        A22   
   1        A23   
   1        A24 

現在，我得到了第三張表（TableC），其結構與TableA相同，但數據不同。

TableC
 --------------------
| ID  | Name  | FK   |
 --------------------
   0     Ab      4
   1     Bb      3
   2     Cb      4
   3     Db      1
   4     Eb      1
  ...

我現在想計算TableA和TableC並將其輸出到一張表中：

例如：

 -----------------------------
| COUNTA  | Status | COUNTC  |
 -----------------------------
   2        A21        2 
   1        A22        0
   1        A23        1
   1        A24        2 

這是我到目前為止所擁有的：

SELECT        SELECT Count(TableA.FK) AS COUNTA, TableB.Status AS Status, Count(TableC.FK) AS COUNTC
FROM            ((TableB LEFT OUTER JOIN
                         TableA ON TableB.PK = TableA.FK) 
LEFT OUTER JOIN TableC ON TableB.PK = TableC.FK)
GROUP BY TableB.Status, TableB.PK;

輸出不正確，CountC與Count A相同：(

Answer 1

您可以將相關查詢添加到第一個查詢中，以得到所需的結果，如下所示：

SELECT Count(TableA.FK) AS COUNTA,
       TableB.Status AS Status,
       (SELECT COUNT(*) FROM TableC where TableC.FK = TableB.PK) as COUNTB
FROM TableB
LEFT JOIN TableA ON TableB.PK = TableA.FK
GROUP BY TableB.Status, TableB.PK;

Answer 2

select TempA.COUNTA , TempA.Status ,TempB.COUNTC from 
( SELECT Count(TableA.FK) AS COUNTA,TableB.Status AS Status ,TableA.FK as PK
     FROM TableB LEFT JOIN TableA ON TableB.PK = TableA.FK
 GROUP BY TableB.Status, TableB.PK) as TempA
 LEFT JOIN 
( SELECT Count(TableC.FK) AS COUNTC,TableA.FK as PK
     FROM TableC LEFT JOIN TableA ON TableC.PK = TableA.FK
 GROUP BY TableA.FK)  as TempB
 ON TempA.PK = TempB.PK)