CODEWITHSUNDEEP
mysqlperformanceselectgroup-by
lomse
lomse

Reputation: 4165

Improve MySQL query for performance

I have this query which runs great on two tables company and question. Both tables are structured in the following way: 

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

I have been trying to figure out how to rewrite this in order to avoid the subquery which seems to slow the query execution. The question tables have over 1000 records. Also, using indexes have decreased the execution time from 545.037 sec to 180.228 sec, still I need improve this.

Thanks

Upvotes: 2

Views: 111

Answers (1)

Bill Karwin
Bill Karwin

Reputation: 562270

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

Upvotes: 2

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