sql - Can this MySQL join query be optimized? -

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i have query takes 27 seconds execute:

select ocal_files.*, count(distinct ocal_favs.username) favs  ocal_files    inner join ocal_favs on ocal_favs.clipart_id = ocal_files.id  group ocal_files.id  order favs desc​

(instead of username should user_id, because have table users)

ocal_files has 37457 rows , ocal_favs has 18263

edit result of explain

mysql> explain select ocal_files.*, count(distinct ocal_favs.username) favs ocal_files inner join ocal_favs on ocal_favs.clipart_i d = ocal_files.id group ocal_files.id order favs desc;                                                                              +----+-------------+------------+--------+----------------+---------+---------+---------------------------------+-------+---------------------------------+ | id | select_type | table      | type   | possible_keys  | key     | key_len | ref                             | rows  |                           | +----+-------------+------------+--------+----------------+---------+---------+---------------------------------+-------+---------------------------------+ |  1 | simple      | ocal_favs  |    | rlb_clipart_id | null    | null    | null                             | 18622 | using temporary; using filesort| |  1 | simple      | ocal_files | eq_ref | primary        | primary | 4       | openclipart.ocal_favs.clipart_id |     1 | using                    | +----+-------------+------------+--------+----------------+---------+---------+---------------------------------+-------+---------------------------------+ 2 rows in set (0.00 sec)

why slow? can optimized? if yes how?

try create index on

ocal_favs ( clipart_id, username )

and make sure there not null constraint on ocal_favs.username or add ocal_favs.username not null condition.

this should allow information ocal_files , index.


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