MySQL query optimization - distinct, order by and limit

Posted by Manuel Darveau on Stack Overflow See other posts from Stack Overflow or by Manuel Darveau
Published on 2010-05-27T03:37:44Z Indexed on 2010/05/27 3:41 UTC
Read the original article Hit count: 276

I am trying to optimize the following query:

select distinct this_.id as y0_
from Rental this_
    left outer join RentalRequest rentalrequ1_ on this_.id=rentalrequ1_.rental_id
    left outer join RentalSegment rentalsegm2_ on rentalrequ1_.id=rentalsegm2_.rentalRequest_id
where
    this_.DTYPE='B'
    and this_.id<=1848978
    and this_.billingStatus=1
    and rentalsegm2_.endDate between 1273631699529 and 1274927699529
order by rentalsegm2_.id asc
limit 0, 100;

This query is done multiple time in a row for paginated processing of records (with a different limit each time). It returns the ids I need in the processing. My problem is that this query take more than 3 seconds. I have about 2 million rows in each of the three tables.

Explain gives:

+----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+----------------------------------------------+
| id | select_type | table        | type   | possible_keys                                       | key           | key_len | ref                                        | rows   | Extra                                        |
+----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+----------------------------------------------+
|  1 | SIMPLE      | rentalsegm2_ | range  | index_endDate,fk_rentalRequest_id_BikeRentalSegment | index_endDate | 9       | NULL                                       | 449904 | Using where; Using temporary; Using filesort | 
|  1 | SIMPLE      | rentalrequ1_ | eq_ref | PRIMARY,fk_rental_id_BikeRentalRequest              | PRIMARY       | 8       | solscsm_main.rentalsegm2_.rentalRequest_id |      1 | Using where                                  | 
|  1 | SIMPLE      | this_        | eq_ref | PRIMARY,index_billingStatus                         | PRIMARY       | 8       | solscsm_main.rentalrequ1_.rental_id        |      1 | Using where                                  | 
+----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+----------------------------------------------+

I tried to remove the distinct and the query ran three times faster. explain without the query gives:

+----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+-----------------------------+
| id | select_type | table        | type   | possible_keys                                       | key           | key_len | ref                                        | rows   | Extra                       |
+----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+-----------------------------+
|  1 | SIMPLE      | rentalsegm2_ | range  | index_endDate,fk_rentalRequest_id_BikeRentalSegment | index_endDate | 9       | NULL                                       | 451972 | Using where; Using filesort | 
|  1 | SIMPLE      | rentalrequ1_ | eq_ref | PRIMARY,fk_rental_id_BikeRentalRequest              | PRIMARY       | 8       | solscsm_main.rentalsegm2_.rentalRequest_id |      1 | Using where                 | 
|  1 | SIMPLE      | this_        | eq_ref | PRIMARY,index_billingStatus                         | PRIMARY       | 8       | solscsm_main.rentalrequ1_.rental_id        |      1 | Using where                 | 
+----+-------------+--------------+--------+-----------------------------------------------------+---------------+---------+--------------------------------------------+--------+-----------------------------+

As you can see, the Using temporary is added when using distinct.

I already have an index on all fields used in the where clause. Is there anything I can do to optimize this query?

Thank you very much!

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