Question

我有三张桌子

表1. color_sets_info 与set_id（PK），set_name列

表2. colors 与set_id（FK），color_id（PK），color_name，color_formula列< / p>

表3. mixed_colors 与color_id1（FK），color_id2（FK），color_formula列

外键colors.set_id引用color_sets_info.set_id

外键mixed_colors.color_id1引用colors.color_id

外键mixed_colors.color_id2引用colors.color_id

如何从 mixed_colors 特定set_name或color_formula以及所有相关列中获取：

colors.color_name（适用于mixed_colors.color_id1），

colors.color_name（适用于mixed_colors.color_id2），

color_sets_info.set_name（对于第一个colors.color_name），

color_sets_info.set_name（第二个colors.color_name）

mixed_colors.color_formula？

例如：

color_sets_info           colors
+--------+-----------+    +--------+----------+------------+---------------+
| set_id | set_name  |    | set_id | color_id | color_name | color_formula |
+--------+-----------+    +--------+----------+------------+---------------+
| 1      | somename1 |    | 1      | 1        | black      | R0G0B0        |
| 2      | somename2 |    | 1      | 2        | yellow     | R255G255B0    |
| 3      | somename3 |    | 2      | 3        | green      | R0G255B255    |
+--------+-----------+    | 3      | 4        | red        | R255G0B0      |
                          +--------+----------+------------+---------------+

mixed_colors
+-----------+-----------+---------------+
| color_id1 | color_id2 | color_formula |
+-----------+-----------+---------------+
| 1         | 4         | R127G0B0      |
| 2         | 3         | R127G255B127  |
| 3         | 1         | R0G127B127    |
+-----------+-----------+---------------+

我需要从 mixed_colors color_formula以及两个set_names和两个color_names获取每种混合颜色，其中1）仅使用 somename1 R127G0B0 公式和 somename2 颜色设置2）

Answer 1

SELECT
    m.color_formula,
    cs1.set_name AS set_name1,
    c1.color_name AS color_name1,
    cs2.set_name AS set_name2,
    c2.color_name AS color_name2
FROM
    mixed_colors m
    JOIN colors c1 ON
        m.color_id1 = c1.color_id
    JOIN color_sets_info cs1 ON
        c1.set_id = cs1.set_id
    JOIN colors c2 ON
        m.color_id2 = c2.color_id
    JOIN color_sets_info cs2 ON
        c2.set_id = cs2.set_id;

或者如果您愿意，可以先将颜色和颜色集合收集到视图中：

CREATE VIEW vw_colors AS
SELECT
    color_id,
    set_id,
    color_name,
    set_name
FROM
    colors c
    JOIN color_sets_info cs ON
        c.set_id = cs.set_id;

然后查询：

SELECT
    m.color_formula,
    v1.set_name AS set_name1,
    v1.color_name AS color_name1,
    v2.set_name AS set_name2,
    v2.color_name AS color_name2
FROM
    mixed_colors m
    JOIN vw_colors v1 ON
        m.color_id1 = v1.color_id
    JOIN vw_colors v2 ON
        m.color_id2 = v2.color_id;

在三个表上使用外键进行SQL查询

1 个答案: