MySQL Forums
Forum List  »  Performance

Very slow query when too many joins
Posted by: As Os
Date: June 05, 2016 09:17AM

In my db I have 2 tables:
1.table 'fields_values' with fields: id,field_id(FK to fields table), ads_id(FK to ads table), value.
2.table 'ads' with fields: id,field_id (which actually is in a json format field).

My query is like this:



SELECT DISTINCT a.*,b.value
FROM ads as a

LEFT JOIN fields_values AS b
ON (`b`.`ads_id` = `a`.`id` AND `b`.field_id="183")

LEFT JOIN fields_values AS c
ON (`c`.`ads_id` = `a`.`id` AND `c`.field_id="183")

Up to 25 joins, it's ok.
But on 26, 27 joins it slows down.
On more joins, it slows down dramatically.

How can I fix this?
(I tried to post the EXPLAIN from phpmyadmin but I failed)

Options: ReplyQuote


Subject
Views
Written By
Posted
Very slow query when too many joins
4329
June 05, 2016 09:17AM
1619
June 05, 2016 09:27AM
1241
June 05, 2016 10:48AM
1242
June 05, 2016 03:33PM
1123
June 06, 2016 02:23AM
1089
June 06, 2016 03:33AM
1095
June 06, 2016 09:02AM
1045
June 06, 2016 11:30AM
1046
June 06, 2016 02:11PM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.