如何提高 mysql COUNT 查询的速度？

Question

如何提高此查询的速度？目前只需要几秒钟就可以加载查询所在的 php 文件，甚至无需查询任何内容。

我有一个关于技能趋势、职位名称和行业的索引。排序规则：utf8mb4_unicode_ci

$sql = "SELECT 
   COUNT(skillsTrends), 
   skillsTrends,
   jobtitle,
   industry,
   industry_url 
FROM fr_skills_trends 
WHERE industry IN ('". implode("', '", $industryInsertSql). "') 
  AND LENGTH(skillsTrends)<=35 
  AND reg_date >= NOW() - INTERVAL 3 MONTH 
GROUP BY skillsTrends ORDER by LENGTH(skillsTrends) DESC";

记录数 < 1,000,000。

Answer 1

试试这个 covering index。

CREATE INDEX fr_skills_trends_date_industry 
          ON fr_skills_trends 
             (reg_date , industry, skillsTrends);

它应该有助于提高查询性能。

而且，您的查询误用了 MySQL's notorious nonstandard extension to GROUP BY。试试这个。

SELECT 
   COUNT(skillsTrends), 
   skillsTrends,
   jobtitle,
   industry,
   industry_url 
FROM fr_skills_trends 
WHERE industry IN ('". implode("', '", $industryInsertSql). "') 
  AND LENGTH(skillsTrends)<=35 
  AND reg_date >= NOW() - INTERVAL 3 MONTH 
GROUP BY skillsTrends, jobtitle, industry, industry_url
ORDER by LENGTH(skillsTrends) DESC

如何提高 mysql COUNT 查询的速度？

How to improve a mysql COUNT query for speed?

php

mysql

sql

count

query-optimization