选择和加入这些表的最有效方法

Question

我有 4 张桌子：

表 1（组）：

id_group  name_group
1         abc
2         def
3         ghi

表2（颜色）：

id_color  name_color
1         blue
2         red
3         green

Table3（品种）：

id_variety id_color id_group name_variety
1          1        1        light
2          3        1        dark
3          6        2        dark

Table4（音调）：

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

给定一个像 1 这样的 id_group，我想做一个选择，结果如下：

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

我能够通过联合解决问题并更改 JOINS 的顺序，但我认为必须有另一种解决方案

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

我认为你想要的更像是：

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

您可以使用全联接代替联合，因为全联接返回第一个表的所有结果以及第二个表的所有结果。

选择 GRO.id_group、COL.id_color、VARI.name_variety、Tone.name_tone 来自 Variety VARI 在 col.id_color=VARI col.id 上加入颜色 COL 在 GRO.id_group=VARI.id_group 上加入 GRO 组 完全加入 Tone on Tone.id_group=GRO.id_group 其中 GRO.id_group = 1