[英]Mysql row number with order by very slow
I have this query我有这个查询
select courses.id, y.qs_world, courses.name_en as name,
courses.description_en as description,
source_link, courses.slug, fee, duration, courses.university_id, college_id,
study_level_id, application_fee, courses.currency_id
from courses
left join university_ranks as y on courses.university_id = y.university_id
and y.year = '2021'
left join universities on courses.university_id = universities.id
left join countries on countries.id = universities.country_id where courses.status = 1
order by ROW_NUMBER() OVER (PARTITION BY countries.id ORDER BY courses.id)
This query is taking too long to execute, but it is working well if I remove the last row.此查询执行时间过长,但如果我删除最后一行,它运行良好。
I used indexing but nothing different.我使用了索引,但没有什么不同。
The EXPLAIN
notes are to Using temporary,Using filesort
but I want to improve the query without using temporary
or filesort
EXPLAIN
说明是Using temporary,Using filesort
但我想改进查询而不使用temporary
或filesort
How can I achieve this?我怎样才能做到这一点?
UPDATE : I tried this query but same speed更新:我试过这个查询,但速度相同
SELECT * FROM (
SELECT
`courses`.`id`,`courses`.`status`, `y`.`qs_world`, `courses`.`name_en` as `name`, `courses`.`description_en` as `description`,
`source_link`, `courses`.`slug`, `fee`, `duration`, `courses`.`university_id`, `college_id`,
`study_level_id`, `application_fee`, `courses`.`currency_id`, `countries`.`id` as country_id
FROM
courses
left join `university_ranks` as `y` on `courses`.`university_id` = `y`.`university_id`
and `y`.`year` = '2021'
left join `universities` on `courses`.`university_id` = `universities`.`id`
left join `countries` on `countries`.`id` = `universities`.`country_id`
) UserCourse where status = 1
order by ROW_NUMBER() OVER (PARTITION BY country_id ORDER BY id)
countries
. countries
。 id
as country_id --> universities
. id
为 country_id --> universities
。 country_id
then remove然后删除
left join `countries` ON `countries`.`id` = `universities`.`country_id`
Move where status = 1
into the inner query.将
where status = 1
移动到内部查询中。
It seems like这好像是
order by ROW_NUMBER() OVER (PARTITION BY country_id ORDER BY id)
could be replaced by可以替换为
ORDER BY country_id, id
Get rid of the outer query摆脱外部查询
Don't say LEFT
unless the 'right' table might have a missing row.除非“右”表可能缺少行,否则不要说
LEFT
。 (It confuses the reader as to your intent.) (它使读者对您的意图感到困惑。)
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