Home/ Questions/Q 1011959
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-16T09:52:19+00:00

I am trying to extract duplicate rows from my database. I have a listings

  • 0

I am trying to extract duplicate rows from my database. I have a listings table and a listings_meta table which holds additional information. The listings_meta table has over 16,000 rows. When I run the query below it runs REALLY slow.

I don’t understand why. Is there something wrong with my code?

SELECT l.id FROM listings AS l
   LEFT JOIN listings_meta AS lm ON lm.listing_id = l.id AND lm.meta_key = 'email'
   LEFT JOIN listings_meta AS lm2 ON lm2.listing_id = l.id AND lm2.meta_key = 'submitter_email'
   WHERE lm.meta_value = 'test@test.com' OR lm2.meta_value = 'test@test.com' OR l.listing_title RLIKE 'Test'
   GROUP BY l.id LIMIT 1

Are there certain things I can do to improve load time of large tables in general?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Indexes

    Do you have any indexes – particularly on LISTINGS_META.listing_id?

    I re-wrote your query as:

       SELECT l.id 
     FROM listings AS l
LEFT JOIN listings_meta AS lm ON lm.listing_id = l.id 
                             AND lm.meta_key = 'email'
                             AND lm.meta_value = 'test@test.com'
LEFT JOIN listings_meta AS lm2 ON lm2.listing_id = l.id 
                              AND lm2.meta_key = 'submitter_email'
                              AND lm2.meta_value = 'test@test.com'
    WHERE l.listing_title RLIKE 'Test'
 GROUP BY l.id LIMIT 1

    WHERE clause

    RLIKE (any of the MySQL regex functionality for that matter) is on par with:

    WHERE l.listing_title LIKE '%Test%'

    Neither can make use of an index on the LISTING.listing_title column…

    The best way to improve the listing_title search would be if the LISTING table is MyISAM, so you could add a Full Text Index to the LISTING.listing_title column in order to use:

    WHERE MATCH(l.listing_title) AGAINST ('Test')

    …but mind that the minimum word length is 3 characters for Full Text Searching (FTS)….

    • 0