Mysql 行號非常慢

Question

我有這個查詢

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)

此查詢執行時間過長，但如果我刪除最后一行，它運行良好。

我使用了索引，但沒有什么不同。

EXPLAIN說明是Using temporary,Using filesort但我想改進查詢而不使用temporary或filesort

我怎樣才能做到這一點？

更新：我試過這個查詢，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) 

Answer 1

• countries 。 id為 country_id --> universities 。 country_id

• 然后刪除

   left join `countries` ON `countries`.`id` = `universities`.`country_id`

• 將where status = 1移動到內部查詢中。

• 這好像是

   order by ROW_NUMBER() OVER (PARTITION BY country_id ORDER BY id)

  可以替換為

   ORDER BY country_id, id

• 擺脫外部查詢

• 除非“右”表可能缺少行，否則不要說LEFT 。 （它使讀者對您的意圖感到困惑。）