mysql - 改进 MySQL 查询以提高性能

Question

我有这个查询，它在两个表company和question. 这两个表的结构如下：

company   |  question
id        |  id
name      |  company_id
          |  sentiment

SELECT company.id as company_id, company.name,  question.sentiment,
(SELECT count(*) FROM question 
WHERE question.sentiment=0 AND question.company_id=company.id) AS count
FROM question
JOIN company ON company.id=question.company_id
 WHERE question.sentiment = 0 GROUP BY company_id ORDER BY count DESC LIMIT 5

我一直在试图弄清楚如何重写它以避免子查询似乎会减慢查询执行速度。问题表有超过 1000 条记录。此外，使用索引已将执行时间从 545.037 秒减少到 180.228 秒，我仍然需要改进这一点。

谢谢

Answer 1

ALTER TABLE question ADD INDEX (sentiment, company_id);

SELECT c.id as company_id, c.name, q.sentiment, q.count
FROM company c
JOIN (
    SELECT company_id, MAX(sentiment) AS sentiment, COUNT(*) AS count
    FROM question
    WHERE sentiment = 0
    GROUP BY company_id
    ORDER BY NULL
) AS q ON c.id = q.company_id
ORDER BY count DESC LIMIT 5