MySQL的：是否有可能加入該羣，BY'd結果兩個選擇α

Question

我有兩個單獨的SELECT語句它們都是GROUP-BY'd分別例如：

SELECT x, y, z FROM a GROUP BY x 
SELECT x, n, o FROM b GROUP BY x 

我非常想加入這兩個共同的SELECT其列，如結合：

SELECT x as x1, y, z FROM a GROUP BY x 
LEFT JOIN (
    SELECT x as x2, n, o FROM b GROUP BY x) 
ON x1=x2; 

這可能嗎？我問，因爲MySQL正在抱怨

您的SQL語法錯誤; 檢查對應 你的MySQL服務器版本使用附近的「LEFT JOIN 的 正確的語法手動選擇 X爲X2

如果這是可能的，任何想法上有什麼錯我的語法？

非常感謝！

Answer 1

這工作

select * from (
    (select 1 a,2 b,3 c) t1 left join (select null a,2 b,5 c) t2 on (t1.b=t2.b) 
); 

另外，

select * from (
    (select 1 a,2 b,3 c) t1 left join (select null a,2 b,5 c) t2 using (b) 
); 

兩個結果

+---+---+---+------+---+---+ 
| a | b | c | a | b | c | 
+---+---+---+------+---+---+ 
| 1 | 2 | 3 | NULL | 2 | 5 | 
+---+---+---+------+---+---+ 
1 row in set (0.00 sec) 

Answer 2

有幾個方法可以做到這一點：

1. 最佳：從兩個查詢作爲子查詢，像這樣

    
   SELECT a.x, y, z, n, o 
       FROM a INNER JOIN b ON a.x = b.x 
   GROUP BY a.x, b.x; 
   

2. 選擇：加入表之前，像這樣的分組

    
   SELECT * 
   FROM  (SELECT x, y, z FROM a GROUP BY x) AS a 
   INNER JOIN (SELECT x, n, o FROM b GROUP BY x) AS b 
        ON a.x = b.x; 
   

Answer 3

你也可以使用此查詢：
SELECT a.x, a.y, a.z, b.x, b.o, b.n FROM a, (SELECT x, n, o FROM b GROUP BY x) as b WHERE a.x = b.x GROUP BY a.x;