MySQL 全文索引查询不使用任何索引？

Question

我有一个像这样创建的简单 table

CREATE TABLE IF NOT EXISTS metadata (
    id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, 
    title varchar(500),
    category varchar(50),
    uuid varchar(20),
    FULLTEXT(title, category)
) ENGINE=InnoDB;

当我执行全文搜索时，100 万行用了 2.5 秒。所以我执行了一个查询规划器，它不使用任何索引：

mysql> explain SELECT uuid, title, category, MATCH(title, category) AGAINST ('grimm' IN NATURAL LANGUAGE MODE) AS score FROM metadata HAVING score > 0 limit 20;
+----+-------------+----------+------------+------+---------------+------+---------+------+---------+----------+-------+
| id | select_type | table    | partitions | type | possible_keys | key  | key_len | ref  | rows    | filtered | Extra |
+----+-------------+----------+------------+------+---------------+------+---------+------+---------+----------+-------+
|  1 | SIMPLE      | metadata | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 1036202 |   100.00 | NULL  |
+----+-------------+----------+------------+------+---------------+------+---------+------+---------+----------+-------+

这是预期的吗？我怎样才能加快速度？

Answer 1

您的查询获取 table 中的每一行，计算自然语言匹配，然后将结果（仍然是每一行）传递给 HAVING 子句。这是 table-扫描。

您应该尝试将全文索引搜索放入 WHERE 子句中，以减少匹配行数。

mysql> explain SELECT uuid, title, category FROM metadata 
    WHERE MATCH(title, category) AGAINST ('grimm' IN NATURAL LANGUAGE MODE) 
    LIMIT 20;

MySQL 全文索引查询不使用任何索引？

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