Why doesn't mysql use my index? - mysql

Question

I have two tables:
mysql> desc myps3t_gameusertrophyinfo;
+-----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| user_id | int(11) | NO | MUL | NULL | |
| trophy_id | int(11) | NO | MUL | NULL | |
| date | datetime | NO | MUL | NULL | |
| date_read | varchar(100) | NO | | NULL | |
+-----------+--------------+------+-----+---------+----------------+
5 rows in set (0.19 sec)
mysql> show index from myps3t_gameusertrophyinfo;
+---------------------------+------------+------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------------------------+------------+------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| myps3t_gameusertrophyinfo | 0 | PRIMARY | 1 | id | A | 4004589 | NULL | NULL | | BTREE | |
| myps3t_gameusertrophyinfo | 0 | user_id | 1 | user_id | A | 7686 | NULL | NULL | | BTREE | |
| myps3t_gameusertrophyinfo | 0 | user_id | 2 | trophy_id | A | 4004589 | NULL | NULL | | BTREE | |
| myps3t_gameusertrophyinfo | 1 | myps3t_gameusertrophyinfo_403f60f | 1 | user_id | A | 7686 | NULL | NULL | | BTREE | |
| myps3t_gameusertrophyinfo | 1 | myps3t_gameusertrophyinfo_61a683d8 | 1 | trophy_id | A | 22624 | NULL | NULL | | BTREE | |
| myps3t_gameusertrophyinfo | 1 | idx_gameusertrophyinfo_date | 1 | date | A | 4004589 | NULL | NULL | | BTREE | |
+---------------------------+------------+------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
7 rows in set (0.06 sec)
the other table:
mysql> desc myps3t_gametrophyinfo ;
+-----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| game_id | int(11) | NO | MUL | NULL | |
| name | varchar(500) | NO | | NULL | |
| desc | varchar(500) | NO | | NULL | |
| type | varchar(20) | NO | | NULL | |
| pic_url | varchar(200) | NO | | NULL | |
| desc_pt | varchar(500) | NO | | NULL | |
| name_pt | varchar(500) | NO | | NULL | |
| hidden_id | int(11) | NO | | NULL | |
| total_id | int(11) | NO | | NULL | |
| trophy_id | int(11) | NO | | NULL | |
| addon_id | int(11) | YES | | NULL | |
| points | double | NO | | 0 | |
| sony_id | int(11) | YES | | NULL | |
+-----------+--------------+------+-----+---------+----------------+
14 rows in set (0.00 sec)
mysql> show index from myps3t_gametrophyinfo;
+-----------------------+------------+-------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-----------------------+------------+-------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| myps3t_gametrophyinfo | 0 | PRIMARY | 1 | id | A | 25976 | NULL | NULL | | BTREE | |
| myps3t_gametrophyinfo | 1 | myps3t_gametrophyinfo_game_id | 1 | game_id | A | 764 | NULL | NULL | | BTREE | |
+-----------------------+------------+-------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
when i do this query:
mysql> explain select * from myps3t_gameusertrophyinfo a, myps3t_gametrophyinfo b where a.trophy_id = b.id and b.addon_id = 58; +----+-------------+-------+--------+--------------------------------------------------------------+---------+---------+-----------------------------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+--------------------------------------------------------------+---------+---------+-----------------------------+---------+-------------+
| 1 | SIMPLE | a | ALL | myps3t_gameusertrophyinfo_61a683d8,myps3t_gameusertrophyinfo | NULL | NULL | NULL | 4004592 | |
| 1 | SIMPLE | b | eq_ref | PRIMARY | PRIMARY | 4 | fabriciols_ps3t.a.trophy_id | 1 | Using where |
+----+-------------+-------+--------+--------------------------------------------------------------+---------+---------+-----------------------------+---------+-------------+
2 rows in set (0.00 sec)
why mysql do not use my keys ?
this query take more than 30 seconds, the first table has 4milion records ...
-- edit --
for quasnoi
mysql> SELECT COUNT(*), COUNT(DISTINCT addon_id), SUM(addon_id = 58) FROM myps3t_gametrophyinfo;
+----------+--------------------------+--------------------+
| COUNT(*) | COUNT(DISTINCT addon_id) | SUM(addon_id = 58) |
+----------+--------------------------+--------------------+
| 25976 | 160 | 6 |
+----------+--------------------------+--------------------+
1 row in set (0.00 sec)

Answer 1

MySQL chooses a as a leading table and b as a driven table. It does use a PRIMARY KEY on b for the joins.
Create an index on myps3t_gametrophyinfo (addon_id), this way b will be more probably chosen as a leading table.

Answer 2

You can try
select * from
myps3t_gametrophyinfo b
STRAIGHT_JOIN myps3t_gameusertrophyinfo a ON (a.trophy_id = b.id)
WHERE b.addon_id = 58;

Answer 3

I would probably rewrite the query to try to get a more sane execution path. I think something like below is more likely to get you the performance you want and is more clear in what you are doing to a human reader
SELECT * FROM myps3t_gametrophyinfo a LEFT JOIN myps3t_gameusertrophyinfo b ON a.id = b.trophy_id WHERE a.addon_id=58;