Question

Please suggest indexes to optimize below query. I couldn’t allowed to rewrite the query but create indexes:

SELECT 
    `ADV`.`inds` as `c0`, 
    sum(`ADVpost`.`clk`) as `m0`
FROM 
    (SELECT *
     FROM advts
     WHERE comp_id = 
        (SELECT comp_id 
         FROM comp 
         WHERE name = 'abc'))  as `ADV`, 
        (SELECT dt_id,
                comp_id,
                b_id,
                ad_id,
                clk,
                resp
         FROM advts_post
         WHERE comp_id = 
                 (SELECT comp_id 
                  FROM comp 
                  WHERE name = 'abc')) as `ADVpost`
WHERE 
    `ADVpost`.`ad_id` = `ADV`.`ad_id`
GROUP BY 
    `ADV`.`inds`
ORDER BY 
    ISNULL(`ADV`.`inds`), `ADV`.`inds` ASC 

The explain for the query is as:

select_type table       type    possible_keys   Extra
PRIMARY     <derived2>  ALL     null            Using temporary; Using filesort
PRIMARY     <derived4>  ALL     null            Using where; Using join buffer
DERIVED     ADVpost     ALL     null            Using where
SUBQUERY    comp        ALL     null            Using where
DERIVED     advts       ALL     null            Using where
SUBQUERY    comp        ALL     null            Using where

Existing indexes are as follows:

ADVpost > PRIMARY KEY (`dt_id`,`comp_id`,`b_id`,`ad_id`)

comp    > PRIMARY KEY (`comp_id`)

advts   > PRIMARY KEY (`ad_id`)

Thanks in advance.

Answer 1

That query is a dogs dinner – whoever wrote it should be severely punished, and the person who said you can’t rewrite it but must make it run faster should be shot.

Loose the sub-selects!

MySQL does not do push-predicates very well (at all?).

Use proper joins instead and state implied joins:

SELECT ap.inds, SUM(ap.clk)
FROM advts_post AS ap
, comp AS co
, advts ad
WHERE ap.comp_id = co.comp_id
AND ad.comp_id = co.comp_id
AND ap.comp_id = ad.comp_id
AND co.name='abc'
GROUP BY ap.inds
ORDER BY ISNULL(ap.inds), ap.inds ASC