將另一個表添加到SQL結果

Question

在這個問題上，我正在絞盡腦汁。 我試圖將數據從另一個表添加到現有的SQL查詢中：

Table Alfa (AA, AB, AC)


Table Zulu (ZA, ZB)

我現有的查詢：

SELECT AB
     , ROUND(AVG(AC),0) AS Srednia
     , COUNT(AC) AS Uzyt 
  FROM Alfa 
 WHERE AA = %s 
 GROUP 
    BY AB 
 ORDER 
    BY AB ASC

如果ZA = AB，如何將ZB添加到結果中？

Answer 1

你是這個意思嗎？

SELECT a.AB, ROUND(AVG(a.AC),0) AS Srednia, COUNT(a.AC) AS Uzyt, Z.ZB FROM Alfa A 
INNER JOIN Zulu Z ON A.AB = Z.ZA
WHERE A.AA = %s
GROUP BY A.AB ORDER BY A.AB ASC

Answer 2

您將把子查詢放在from子句中作為派生表：

SELECT
  a.AB,
  a.Srednia,
  a.Uzyt,
  z.ZB
FROM
(
  SELECT AB
       , ROUND(AVG(AC),0) AS Srednia
       , COUNT(AC) AS Uzyt 
    FROM Alfa 
   WHERE AA = %s 
   GROUP BY AB 
) a
JOIN Zulu z ON z.ZA = a.AB
ORDER BY a.AB ASC;