[英]MySQL fulltext index query does not use any index?
我有一個像這樣創建的簡單表
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;
當我執行全文搜索時,1M 行需要 2.5 秒。 所以我執行了一個查詢規划器,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 |
+----+-------------+----------+------------+------+---------------+------+---------+------+---------+----------+-------+
這是預期的嗎? 我怎樣才能加快速度?
您的查詢獲取表中的每一行,計算自然語言匹配,然后將結果(仍然針對每一行)傳遞給 HAVING 子句。 這是表掃描。
您應該嘗試將全文索引搜索放入 WHERE 子句中,以減少匹配行的數量。
mysql> explain SELECT uuid, title, category FROM metadata
WHERE MATCH(title, category) AGAINST ('grimm' IN NATURAL LANGUAGE MODE)
LIMIT 20;
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