Question

I would like to know the impact on performance if I run this query in the following conditions.

Query:

select   `players`.*, count(`clicks`.`id`) as `clicks_count` 
from     `players` left join `clicks` on `clicks`.`player_id` = `players`.`id`
group by `players`.`id`
order by `clicks_count` desc 
limit    1

Conditions:

1. In the clicks table I expect to get
   insert 1000 times in a 1 minute
2. The clicks table will contain more
   then 1,000,000 rows
3. The players table will contain
   10,000 rows
4. The players table get inserted into every 5
   minutes

I would like to know what to expect performance-wise if I run the query 1000 times in 1 minute.

Thanks

Answer 1

That query will never run in milliseconds with any meaningful amounts of data in your tables. It’ll run two full table scans, join the two together, aggregate the mess, and fetch the top row from that.

Use a trigger to store the total in the players, and index that field. You’ll then be able to avoid the join altogether:

select p.* from players p order by clicks_count desc limit 1