MYSQL, very slow order by

Question

I have got two tables. One is a User table with a primary key on the userid and the other table references the user table with a foreign key.

The User table has only

Answer 1

First try to get result based on primary key with out join and use result to query result again.
For ex:

$userIds=mysql::select("select user_id from photo ORDER BY p0_.uploaddate DESC Limit 10 OFFSET 100000");

$photoData=mysql::select("SELECT p0_., p1_. FROM photo p0_, User p1_ WHERE p0_.user_id = p1_.user_id and p0_.user_id in ($userIds->user_id) order by p0_.uploaddate");

Here we had divided the statement into two parts:
1.We can easily order and get based on primary key and also there are no joins.
2.Getting query results based on id and order by is only on limited columns we can retrieve data in less time

Answer 2

From 30 seconds to 0.015 sec / 0.000 sec using Quassnoi answer ! This is what I called MySql expertise ! I cut out one Join from my personal project (no join with itself)

Select ser.id_table, ser.id_rec, ser.relevance, cnt, title, description, sell_url, medium_thumb,  
        unique_id_supplier, keywords width, height, media_type 
from (    
        Select ser.id_rec, ser.id_table, ser.relevance, ser.cnt 
        from searchEngineResults ser     
        where thisSearch = 16287     
    order by  ser.relevance desc, cnt desc, id_rec 
    ) ser 
join photo_resell sou on sou.id = ser.id_rec 
#join searchEngineResults ser on ser.id_rec = tmp.id_rec 
limit 0, 9

Answer 3

You need a separate index on uploaddate. This sort will take advantage of composite index only if uploaddate is first column in it. You can also try to add user_id to ORDER BY:

    ....      
    ORDER BY p0_.user_id, p0_.uploaddate

Answer 4

You have two problems:

1. You need to create an INDEX(user_id, uploaddate) which will greatly increase the efficiency of the query.

2. You need to find a workaround to using LIMIT 10 OFFSET 100000. MySQL is creating a recordset with 100,000 records in it, then it pulls the last 10 records off the end... that is extremely inefficient.

https://www.percona.com/blog/2006/09/01/mysql-order-by-limit-performance-optimization/

Answer 5

Seems you're suffering from MySQL's inability to do late row lookups:

• MySQL ORDER BY / LIMIT performance: late row lookups
• Late row lookups: InnoDB

Try this:

SELECT  p.*, u.*
FROM    (
        SELECT  id
        FROM    photo
        ORDER BY
                uploaddate DESC, id DESC
        LIMIT   10
        OFFSET  100000
        ) pi
JOIN    photo p
ON      p.id = pi.id
JOIN    user u
ON      u.user_id = p.user_id