mysql - 来自使用 GROUP_CONCAT() 打包的 Tri-INNER JOIN-Relation 的重复值

Question

我应该得到以下行

[id -              gamma             -              omega            ]
[1  - Gamma1, Gamma2, Gamma3, Gamma4 - Omega1, Omega2, Omega3, Omega4]

但我得到的结果显示在 SQLFiddle 上

如果我删除了 SET 并保留了它的 GROUP_CONCAT()，它会正常工作。

为什么关系会相互作用并产生重复值？

SQL:

SELECT a.id, 
       GROUP_CONCAT(g.name) AS gamma, 
       GROUP_CONCAT(o.name) AS omega 
FROM alpha a

     #SET A.O.
     INNER JOIN alpha_omega ao ON ao.alpha_id = a.id 
     INNER JOIN omega o ON o.id = ao.omega_id 

     #SET A.G.
     INNER JOIN alpha_gamma ag ON ag.alpha_id = a.id 
     INNER JOIN gamma g ON g.id = ag.gamma_id

WHERE a.id = 1
GROUP BY a.id

Answer 1

可能是正确的连接(不使用 GROUP_CONCAT(DISTINCT ...)):

SELECT a.id, GROUP_CONCAT(o.name) AS omega  
FROM alpha a
JOIN delta d ON d.alpha_id = a.id 
JOIN omega o ON o.id = d.omega_id 
GROUP BY a.id
UNION ALL
SELECT a.id, GROUP_CONCAT(g.name) AS gamma
FROM alpha a
JOIN beta b ON b.alpha_id = a.id 
JOIN gamma g ON g.id = b.gamma_id
GROUP BY a.id;

在一行内:

SELECT id, MIN(gamma) AS gamma, MIN(omega) AS omega
FROM (
SELECT a.id, NULL AS gamma, GROUP_CONCAT(o.name ORDER BY o.name) AS omega  
  FROM alpha a
  JOIN delta d ON d.alpha_id = a.id 
  JOIN omega o ON o.id = d.omega_id
  GROUP BY a.id
  UNION ALL
  SELECT a.id, GROUP_CONCAT(g.name ORDER BY g.name) AS gamma, NULL
  FROM alpha a
  JOIN beta b ON b.alpha_id = a.id 
  JOIN gamma g ON g.id = b.gamma_id
  GROUP BY a.id
) sub
GROUP BY id;

SQL Fiddle Demo