[英]MySQL fulltext index query does not use any index?
我有一个像这样创建的简单表
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,1M 行需要 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?
您的查询获取表中的每一行,计算自然语言匹配,然后将结果(仍然针对每一行)传递给 HAVING 子句。 这是表扫描。
您应该尝试将全文索引搜索放入 WHERE 子句中,以减少匹配行的数量。
mysql> explain SELECT uuid, title, category FROM metadata
WHERE MATCH(title, category) AGAINST ('grimm' IN NATURAL LANGUAGE MODE)
LIMIT 20;
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