私はテーブルを作成しています
create table temp_test2 (
date_id int(11) NOT NULL DEFAULT '0',
`date` date NOT NULL,
`day` int(11) NOT NULL,
PRIMARY KEY (date_id)
);
create table temp_test1 (
date_id int(11) NOT NULL DEFAULT '0',
`date` date NOT NULL,
`day` int(11) NOT NULL,
PRIMARY KEY (date_id)
);
explain select * from temp_test as t inner join temp_test2 as t2 on (t2.date_id =t.date_id) limit 3;
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
| 1 | SIMPLE | t | ALL | date_id | NULL | NULL | NULL | 4 | NULL |
| 1 | SIMPLE | t2 | ALL | date_id | NULL | NULL | NULL | 4 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
code_id
両方のテーブルでキーが使用されていない理由ですがcode_id=something
、条件付きで使用するとキーを使用しているため、
explain select * from temp_test as t inner join temp_test2 as t2 on (t2.date_id =t.date_id and t.date_id =1) limit 3;
+----+-------------+-------+-------+-------------------------------------+---------+---------+-------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+-------------------------------------+---------+---------+-------+------+-------+
| 1 | SIMPLE | t | const | PRIMARY,date_id,date_id_2,date_id_3 | PRIMARY | 4 | const | 1 | NULL |
| 1 | SIMPLE | t2 | ref | date_id,date_id_2,date_id_3 | date_id | 4 | const | 1 | NULL |
+----+-------------+-------+-------+-------------------------------------+---------+---------+-------+------+-------+
(unique,composite primary,composite) キーも試しましたが、機能しません。なぜこれがそうなのか、誰でも説明できますか?