Mysql Explain Ïê½â[Ç¿ÁÒÍÆ¼ö]
Mysql Explain Ïê½â
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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 | |
+----+-------------+------------+--------+-------------------+---------+---------+------+------+-------+
ºÜÏÔÈ»ÕâÌõSQLÊÇ´ÓÀïÏòÍâµÄÖ´ÐÐ,¾ÍÊÇ´Óid=3 ÏòÉÏÖ´ÐÐ.
2. select_type
¾ÍÊÇselectÀàÐÍ,¿ÉÒÔÓÐÒÔϼ¸ÖÖ
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