performance - How to tune self-join table in mysql like this? -


i have table i'm trying select , date. query took 2 min run on 4 million records. i'm not sure how more can squeeze out of query. 

    select c.fk_id, c.from_date, c.fk_pb, min(o.from_date) to_date       table_x c           inner join table_x o on c.fk_id =  o.fk_id , c.fk_pb = o.fk_pb   o.from_date > c.from_date           group c.fk_id, c.from_date, c.fk_pb

there indexes on from_date, fk_pb , fk_id already.

the schema this.

+-----------------------------+---------------+------+-----+---------+-------+ | field                       | type          | null | key | default | | +-----------------------------+---------------+------+-----+---------+-------+ | fk_id                       | int(11)       | yes  | mul | null    |       | | fk_pb                       | int(11)       | yes  | mul | null    |       | | from_date                   | date          | yes  | mul | null    |       | | to_date                     | date          | yes  |     | null    |       | +-----------------------------+---------------+------+-----+---------+-------+

i know should not use self-join @ in mysql, data comes , i'm trying find best way select , date out of table. if there's else make 1 faster that'd great.

thanks lot.

updated

+----+-------------+-------+------+----------------------------------------------------------------------+-------------------------+---------+----------------------------------------+---------+----------------------------------------------+ | id | select_type | table | type | possible_keys                                                        | key                     | key_len | ref                                    | rows    |                                        | +----+-------------+-------+------+----------------------------------------------------------------------+-------------------------+---------+----------------------------------------+---------+----------------------------------------------+ |  1 | simple      | c     |  | idx_fk_pb,idx_fk_id,idx_frm_date                                     | null                    | null    | null                                   | 4527750 | using where; using temporary; using filesort | |  1 | simple      | o     | ref  | idx_fk_pb,idx_fk_id,idx_frm_date                                     | idx_fk_id               | 5       | db.c.fk_id                             |     110 | using                                  | +----+-------------+-------+------+----------------------------------------------------------------------+-------------------------+---------+----------------------------------------+---------+----------------------------------------------+

adding index relevant columns speeds up:

index(fk_id, fk_pb,from_date)

which performs better because:

  • mysql can use index rows c, doesn't need go table (adding column not in index slow down again bit).
  • mysql pretty bad @ index merging, , chooses not use (luckily), , when it's suboptimal.
  • well, index covering search (in case, join on = searching for) faster mysql electing 1 of indexes (the restrictive one, show index tablename can show cardinality) on separate columns use , having scan values in other columns.

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