來選擇並加入這些表的最有效方法

Question

我有4個表：

表1（組）：

id_group name_group 
1   abc 
2   def 
3   ghi 

表2（彩色）：

id_color name_color 
1   blue 
2   red 
3   green 

表3（綜藝）： （調）：

id_tone id_color id_group name_tone 
1   1  1  ocean 
2   5  1  sea 
3   9  3  clay 

鑑於像1的id_group我要做出選擇導致這樣的事情：

id_group id_color name_variety name_tone 
1  1  light  ocean 
1  3  dark   NULL 
1  5  NULL   sea 

我能夠與聯盟來解決問題和改變的順序JOINS但我認爲必須有另一種解決方案

SELECT 
    GRO.id_group, COL.id_color, VARI.name_variety, TONE.name_tone 
FROM 
    groups GRO 
LEFT OUTER JOIN 
    variety VARI ON (VARI.id_group = GRO.id_group) 
LEFT OUTER JOIN 
    tone TONE ON (TONE.id_group = GRO.id_group) 
       AND (TONE.id_color = VARI.id_color) 
LEFT OUTER JOIN 
    color COL ON (COL.id_color = VARI.id_color) 
       OR (COL.id_color = TONE.id_color) 
WHERE 
    GRO.id_group = 1 

UNION 

SELECT 
    GRO.id_group, COL.id_color, VARI.name_variety, TONE.name_tone 
FROM 
    groups GRO 
LEFT OUTER JOIN 
    tone TONE ON (TONE.id_group = GRO.id_group) 
LEFT OUTER JOIN 
    variety VARI ON (VARI.id_group = GRO.id_group) 
       AND (VARI .id_color = TONE.id_color) 
LEFT OUTER JOIN 
    color COL ON (COL.id_color = VARI.id_color) 
       OR (COL.id_color = TONE.id_color) 
WHERE 
    GRO.id_group = 1 

Answer 1

我想你想要的是更多的東西一樣：

SELECT 
    id_group, 
    id_color, 
    MAX(max_variety), 
    MAX(max_tone) 
FROM 
    (SELECT 
     v.id_group, 
     v.id_color, 
     MAX(name_variety) AS max_variety, 
     MAX(name_tone) AS max_tone 
    FROM 
     variety V INNER JOIN 
     color c ON 
     V.id_color = c.id_color LEFT OUTER JOIN 
     tone t ON 
     t.id_group = v.id_group AND 
     t.id_color = V.id_color 
    WHERE 
     v.id_group = 1 
    GROUP BY 
     v.id_group, 
     v.id_color 

    UNION ALL 

    SELECT 
     t.id_group, 
     t.id_color, 
     MAX(name_variety) AS max_variety, 
     MAX(name_tone) AS max_tone 
    FROM 
     tone t INNER JOIN 
     color c ON 
     t.id_color = c.id_color LEFT OUTER JOIN 
     variety V ON 
     v.id_group = t.id_group AND 
     v.id_color = t.id_color 
    WHERE 
     t.id_group = 1 
    GROUP BY 
     t.id_group, 
     t.id_color) u 
GROUP BY 
    id_group, 
    id_color 

Answer 2

而不是使用聯合可以使用完全聯接，因爲完全聯接返回第一個表的所有結果以及第二個表的所有結果。

SELECT GRO.id_group，COL.id_color，VARI.name_variety，Tone.name_tone從品種VARI 上col.id_color聯接顏色COL = VARI col.id 上GRO.id_group = VARI.id_group 加入羣組GRO Tone.id_group = GRO.id_group 其中GRO.id_group = 1