Я обнаружил очень странное поведение mysql: когда я запускаю определенный запрос дважды, объяснение этого запроса отличается во второй раз:
query = SELECT `twstats_twwordstrend`.`id`, `twstats_twwordstrend`.`created`, `twstats_twwordstrend`.`freq`, `twstats_twwordstrend`.`word_id` FROM `twstats_twwordstrend` INNER JOIN `twstats_twwords` ON (`twstats_twwordstrend`.`word_id` = `twstats_twwords`.`id`) WHERE (`twstats_twwords`.`name` = '@ladygaga' AND `twstats_twwordstrend`.`created` > '2011-01-28 01:30:19' );
1st query execution and then run explain :
mysql> EXPLAIN SELECT `twstats_twwordstrend`.`id`, `twstats_twwordstrend`.`created`, `twstats_twwordstrend`.`freq`, `twstats_twwordstrend`.`word_id` FROM `twstats_twwordstrend` INNER JOIN `twstats_twwords` ON (`twstats_twwordstrend`.`word_id` = `twstats_twwords`.`id`) WHERE (`twstats_twwords`.`name` = '@ladygaga' AND `twstats_twwordstrend`.`created` > '2011-01-28 01:30:19' );
+----+-------------+----------------------+--------+-------------------------------+---------+---------+-------------------------------------------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------------------+--------+-------------------------------+---------+---------+-------------------------------------------+---------+-------------+
| 1 | SIMPLE | twstats_twwordstrend | ALL | twstats_twwordstrend_4b95d890 | NULL | NULL | NULL | 4877401 | Using where |
| 1 | SIMPLE | twstats_twwords | eq_ref | PRIMARY | PRIMARY | 4 | statweestics.twstats_twwordstrend.word_id | 1 | Using where |
+----+-------------+----------------------+--------+-------------------------------+---------+---------+-------------------------------------------+---------+-------------+
2 rows in set (0.00 sec)
2nd query execution and then run explain :
mysql> EXPLAIN SELECT `twstats_twwordstrend`.`id`, `twstats_twwordstrend`.`created`, `twstats_twwordstrend`.`freq`, `twstats_twwordstrend`.`word_id` FROM `twstats_twwordstrend` INNER JOIN `twstats_twwords` ON (`twstats_twwordstrend`.`word_id` = `twstats_twwords`.`id`) WHERE (`twstats_twwords`.`name` = '@ladygaga' AND `twstats_twwordstrend`.`created` > '2011-01-28 01:30:19' );
+----+-------------+----------------------+------+-------------------------------+-------------------------------+---------+---------------------------------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------------------+------+-------------------------------+-------------------------------+---------+---------------------------------+--------+-------------+
| 1 | SIMPLE | twstats_twwords | ALL | PRIMARY | NULL | NULL | NULL | 222994 | Using where |
| 1 | SIMPLE | twstats_twwordstrend | ref | twstats_twwordstrend_4b95d890 | twstats_twwordstrend_4b95d890 | 4 | statweestics.twstats_twwords.id | 15 | Using where |
+----+-------------+----------------------+------+-------------------------------+-------------------------------+---------+---------------------------------+--------+-------------+
2 rows in set (0.00 sec)
mysql> describe twstats_twwords;
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| created | datetime | NO | | NULL | |
| name | varchar(140) | NO | | NULL | |
+---------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> describe twstats_twwordstrend;
+---------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+----------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| created | datetime | NO | | NULL | |
| freq | double | NO | | NULL | |
| word_id | int(11) | NO | MUL | NULL | |
+---------+----------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
Как это может быть возможно?