MySQL ignore index even with use index or force index

Question

Here I'll add part of my query because it's sensitive information and I will use not real names:

SELECT
  `entity`.`id`,
  `entity`.`requirements`,
  `entity`.`description`,
  `entity`.`status`,
  `entity_videos`.`length`,
  `entity_videos`.`quality`,
  `states`.`name`,
  `uploads`.`id`,
  `uploads`.`name`
    FROM  `entity`
    LEFT JOIN  `states`  ON `states`.`id` = `entity`.`state_id`
    INNER JOIN  `uploads` FORCE INDEX (`uploadable_id_index`)
       ON  `uploads`.`uploadable_type` = 'Entity'
      AND  `uploads`.`category` = 'Icon'
      AND  (`uploads`.`uploadable_id` = `entity`.`id`
              OR  `uploads`.`uploadable_id` = `entity`.`parent_entity_for_icon`
           )
    INNER JOIN  `entity_videos` FORCE INDEX (entity_videos_entity_id_index)
       ON `entity_videos`.`entity_id` = `entity`.`id`
    WHERE  `entity`.`status` = 'active' 

The issue is that Mysql optimizer do not want to use uploadable_id_index index. Part of explain:

As I know FORCE INDEX is force optimizer to use index except for situation that optimizer can't use the index. What should I do to force that index and do not make a full scan of the table? I tried to remove entity_videos_entity_id_index also I tried to add uploads table information to where clause, but nothing works for me. Any ideas? Thank you very much for any help

Updated:

With help of @Barmar and @PaulSpiegel I found that issue is in (uploads.uploadable_id = entity.id OR uploads.uploadable_id = entity.parent_entity_for_icon) . And playing with query for some time I found that best solution in my case is:

 SELECT
  `entity`.`id`,
  `entity`.`requirements`,
  `entity`.`description`,
  `entity`.`status`,
  `entity_videos`.`length`,
  `entity_videos`.`quality`,
  `states`.`name`,
  `icon`.`id`,
  `icon`.`name`,
  `parent_offer_icon`.`id`,
  `parent_offer_icon`.`name`
    FROM  `entity`
    LEFT JOIN  `states`  ON `states`.`id` = `entity`.`state_id`
    LEFT JOIN  `uploads` as `icon` FORCE INDEX (`uploadable_id_index`)
       ON  `icon`.`uploadable_type` = 'Entity'
      AND  `icon`.`category` = 'Icon'
      AND  `icon`.`uploadable_id` = `entity`.`id`
    LEFT JOIN  `uploads` as `parent_offer_icon` FORCE INDEX (`uploadable_id_index`)
       ON  `parent_offer_icon`.`uploadable_type` = 'Entity'
      AND  `parent_offer_icon`.`category` = 'Icon'
      AND  `parent_offer_icon`.`uploadable_id` = `entity`.`parent_entity_for_icon`
    INNER JOIN  `entity_videos` FORCE INDEX (entity_videos_entity_id_index)
       ON  `entity_videos`.`entity_id` = `entity`.`id`
    WHERE  `entity`.`status` = 'active'
      AND  (parent_offer_icon.id IS NOT NULL
              OR  icon.id IS NOT NULL ) 

I'm still open for other suggestions :)

Answer 1

Let's start by turning the pesky OR into UNION :

( SELECT  e.id AS eid,
          u.id AS uid,
          u.name AS uname
    FROM `uploads` AS u 
    INNER JOIN  `entity` AS e
       ON  u.`uploadable_id` = e.`id`
    WHERE  u.`uploadable_type` = 'Entity'
      AND  u.`category` = 'Icon'
      AND  e.status = 'active'
) UNION DISTINCT
( SELECT  e.id AS eid,
          u.id AS uid,
          u.name AS uname
    FROM `uploads` AS u 
    INNER JOIN   `entity` AS e
       ON  u.`uploadable_id` = e.`parent_entity_for_icon` 
    WHERE  u.`uploadable_type` = 'Entity'
      AND  u.`category` = 'Icon'
      AND  e.status = 'active'
)

That will need some of these indexes:

uploads:  INDEX(uploadable_type, category, uploadable_id, id, name)
entity:   INDEX(parent_entity_for_icon, status, id)

(I assume entity has PRIMARY KEY(id) ? Please provide SHOW CREATE TABLE so I don't have to guess.) If there are problems with such a long index, let me know; I can probably provide a workaround.

By turning the OR into a UNION , different indexes can be used for each part. With OR , the Optimizer usually punts and does something inefficient.

Please verify that the query above runs fast and produces reasonable output. Then...

SELECT  e.`id`, e.`requirements`, e.`description`, e.`status`,
        ev.`length`, ev.`quality`,
        s.`name`,
        uid, uname
    FROM ( the-query-above ) AS i
    JOIN `entity` AS e  ON e.id = i.eid
    LEFT JOIN  `states` AS s  ON s.`id` = e.`state_id`
    INNER JOIN  `entity_videos` AS ev  ON ev.`entity_id` = i.eid

Other than PRIMARY KEY(id) on each table, you will need

entity_videos:  INDEX(entity_id)  -- good, or
entity_videos:  INDEX(entity_id, length, quality)  -- better ("covering")

Don't use FORCE INDEX .

More on index creation: http://mysql.rjweb.org/doc.php/index_cookbook_mysql