Mysql Explain Ïê½â

Mysql Explain Ïê½â
ת×ÔITPUBhttp://www.itpub.net/viewthread.php?tid=1034410&extra=page%3D1%26amp%3Bfilter%3Ddigest&page=1
Ò».Óï·¨
explain < table_name >
ÀýÈç: explain select * from t3 where id=3952602;
¶þ.explainÊä³ö½âÊÍ
+----+-------------+-------+-------+-------------------+---------+---------+-------+------+-------+
| id | select_type | table | type  | possible_keys     | key     | key_len | ref   | rows | Extra |
+----+-------------+-------+-------+-------------------+---------+---------+-------+------+-------+
1.id
  ÎÒµÄÀí½âÊÇSQLÖ´ÐеÄ˳ÀûµÄ±êʶ,SQL´Ó´óµ½Ð¡µÄÖ´ÐÐ.
ÀýÈç:
mysql> explain select * from (select * from ( select * from t3 where id=3952602) a) b;
+----+-------------+------------+--------+-------------------+---------+---------+------+------+-------+
| id | select_type | table      | type   | possible_keys     | key     | key_len | ref  | rows | Extra |
+----+-------------+------------+--------+-------------------+---------+---------+------+------+-------+
|  1 | PRIMARY     | <derived2> | system | NULL              | NULL    | NULL    | NULL |    1 |       |
|  2 | DERIVED     | <derived3> | system | NULL              | NULL    | NULL    | NULL |    1 |       |
|  3 | DERIVED     | t3         | const  | PRIMARY,idx_t3_id | PRIMARY | 4       |      |    1 |       |
+----+-------------+------------+--------+-------------------+---------+---------+------+------+------