您能否解释一下使用 Composite MySQL INDEX 进行多个 INNER JOIN 的方面？

Question

查询为

SELECT v.value
FROM products
         JOIN products_attributes_options pao
              ON 1 = 1
                  AND products.id = pao.product_id
         JOIN attributes_options ao
              ON 1 = 1
                  AND pao.attribute_option_id = ao.id
                  AND attribute_id = 12
         JOIN attributes_options_values aov
              ON
                      1 = 1
                      AND ao.id = aov.attribute_option_id
         JOIN `values` v
              ON
                      1 = 1
                      AND aov.value_id = v.id

         JOIN values_words vw_1
              ON
                      1 = 1
                      AND v.id = vw_1.value_id
         JOIN values_words vw_2
              ON
                      1 = 1
                      AND v.id = vw_2.value_id

         JOIN words w_1
              ON
                      1 = 1
                      AND vw_1.word_id = w_1.id
                      AND w_1.value LIKE '%a%'
         JOIN words w_2
              ON
                      1 = 1
                      AND vw_2.word_id = w_2.id
                      AND w_2.value LIKE '%a%'

GROUP BY v.id, v.value
ORDER BY v.id, v.value

对于这部分查询

JOIN products_attributes_options pao
     ON 1 = 1
        AND products.id = pao.product_id
JOIN attributes_options ao
     ON 1 = 1
        AND pao.attribute_option_id = ao.id
        AND attribute_id = 12

我有复合索引

ix_aov_p (attribute_option_id, product_id)
ix_p_aov (product_id, attribute_option_id)

通过 EXPLAIN 我看到的查询 - 其中两个可能是键。但是我觉得只有ix_aov_p就够了。

您能否解释一下复合索引如何适用于这些情况？我需要两个索引还是只需要一个索引？我需要使用其中的哪一个？ ix_aov_p 或 ix_p_aov

我研究过类似的问题，但没有足够的解释来理解 - 会发生什么？

Separate Join clause in a Composite Index - 类似问题 - 已接受的答案没有充分解释发生的情况以及复合 INDEX 不起作用的原因。

很高兴解释这些 JOIN 从 INDEX 端发生了什么，以理解在这种情况下使用的复合 INDEX。

数据库转储要使用的表 - DUMP（结构）

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  `product_id` int(11) NOT NULL,
  `attribute_option_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `ix_p_aov` (`product_id`,`attribute_option_id`),
  UNIQUE KEY `ix_aov_p` (`attribute_option_id`,`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
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Answer 1

这太正常化了。

如果 Products table 有很多信息——名称、大小等，那么用 product_id 规范化 product 是很好的。但我只看到name。所以去掉 product_id 和 Products 只剩下一列 product_name.

完成后，确定 many:many 映射 table。他们不需要 id，只需要两列，每列要么是一个 id 要么是一个值。有关此类 tables 的最佳复合索引的建议，请参阅此内容：http://mysql.rjweb.org/doc.php/index_cookbook_mysql#many_to_many_mapping_table

But I thought only ix_aov_p is enough.

这为 "given an aov, find the p values" 提供了一种有效的方法。在其他情况下，您需要相反的顺序。复合索引是有序的。在这样的映射 table 的情况下， "given" 必须排在第一位。

在其他一些情况下，顺序很重要：

WHERE b > 4 AND a = 8

需要 INDEX(a, b) 按此顺序。它可以快速找到 a=8 和 b=4 的所有条目，它们向前扫描直到 a>8。考虑搜索 lastname='James' 和 firstname LIKE 'R%'.

与此同时，INDEX(a,b) 的任一顺序都适合

WHERE b = 4 AND a = 8

更多讨论：http://mysql.rjweb.org/doc.php/index_cookbook_mysql

您能否解释一下使用 Composite MySQL INDEX 进行多个 INNER JOIN 的方面？

Could you explain aspect of using Composite MySQL INDEX for multiple INNER JOIN?

mysql

database

indexing

join

compound-index