Question

此查询需要一分钟才能完成：

SELECT keyword, count(*) as 'Number of Occurences'
    FROM movie_keyword
    JOIN
    keyword
    ON keyword.`id` = movie_keyword.`keyword_id`
    GROUP BY keyword
    ORDER BY count(*) DESC
    LIMIT 5

每个关键字都有一个与之关联的ID（keyword_id列）。该ID用于从关键字表中查找实际关键字。

movie_keyword有280万行

关键字有127,000

然而，要返回最常用的keyword_id，只需1秒钟：

SELECT keyword_id, count(*)
    FROM movie_keyword
    GROUP BY keyword_id
    ORDER BY count(*) DESC
    LIMIT 5

有更有效的方法吗？

使用EXPLAIN输出：

1   SIMPLE  keyword ALL PRIMARY NULL    NULL    NULL    125405  Using temporary; Using filesort
1   SIMPLE  movie_keyword   ref idx_keywordid   idx_keywordid   4   imdb.keyword.id 28  Using index

结构：

CREATE TABLE `movie_keyword` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `movie_id` int(11) NOT NULL,
  `keyword_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idx_mid` (`movie_id`),
  KEY `idx_keywordid` (`keyword_id`),
  KEY `keyword_ix` (`keyword_id`),
  CONSTRAINT `movie_keyword_keyword_id_exists` FOREIGN KEY (`keyword_id`) REFERENCES `keyword` (`id`),
  CONSTRAINT `movie_keyword_movie_id_exists` FOREIGN KEY (`movie_id`) REFERENCES `title` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4256379 DEFAULT CHARSET=latin1;

CREATE TABLE `keyword` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `keyword` text NOT NULL,
  `phonetic_code` varchar(5) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `idx_keyword` (`keyword`(5)),
  KEY `idx_pcode` (`phonetic_code`),
  KEY `keyword_ix` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=127044 DEFAULT CHARSET=latin1;

Answer 1

未经测试但在我看来应该工作并且明显更快，不太确定你是否允许在mysql的子查询中使用限制，但还有其他方法。

SELECT keyword, count(*) as 'Number of Occurences'
    FROM movie_keyword
    JOIN
    keyword
    ON keyword.`id` = movie_keyword.`keyword_id`
    WHERE movie_keyword.keyword_id IN (
        SELECT keyword_id
        FROM movie_keyword
        GROUP BY keyword
        ORDER BY count(*) DESC    
        LIMIT 5
    )
    GROUP BY keyword
    ORDER BY count(*) DESC;

这应该更快，因为你没有将movie_keyword中280万个条目与关键字一起加入，只是那些实际匹配的条目，我猜这些条目要少得多。

编辑，因为mysql不支持您必须运行的子查询内的限制

SELECT keyword_id
FROM movie_keyword
GROUP BY keyword
ORDER BY count(*) DESC    
LIMIT 5;

首先在获取结果后运行第二个查询

SELECT keyword, count(*) as 'Number of Occurences'
    FROM movie_keyword
    JOIN
    keyword
    ON keyword.`id` = movie_keyword.`keyword_id`
    WHERE movie_keyword.keyword_id IN (RESULTS_FROM_FIRST_QUERY_SEPARATED_BY_COMMAS)
    GROUP BY keyword
    ORDER BY count(*) DESC;

使用您正在使用的任何语言以编程方式将RESULTS_FROM_FIRST_QUERY_SEPARATED_BY_COMMAS替换为正确的值

Answer 2

查询似乎没问题，但我认为结构不是，试着给列上的索引

keyword.id

试，

CREATE INDEX keyword_ix ON keyword (id);

或

ALTER TABLE keyword ADD INDEX keyword_ix (id);

如果您可以发布表格的结构，那么

会好得多：keyword和Movie_keyword。哪两个是主表和引用表？

SELECT keyword, count(movie_keyword.id) as 'Number of Occurences'
FROM movie_keyword
     INNER JOIN  keyword
           ON keyword.`id` = movie_keyword.`keyword_id`
GROUP BY keyword
ORDER BY 'Number of Occurences' DESC
LIMIT 5

Answer 3

我知道这是一个非常古老的问题，但是因为我认为xception忘记了mysql中的交付表，我想提出另一个解决方案。它只需要一个查询，它省略了加入大数据。如果有人拥有如此大的数据并且可以测试它（可能是问题创建者），请分享结果。

SELECT keyword.keyword, _temp.occurences
FROM (
  SELECT keyword_id, COUNT( keyword_id ) AS occurences
  FROM movie_keyword
  GROUP BY keyword_id
  ORDER BY occurences DESC 
  LIMIT 5
) AS _temp
JOIN keyword ON _temp.keyword_id = keyword.id
ORDER BY _temp.occurences DESC

MySQL JOIN时间缩短

3 个答案: