mysql慢查詢最佳化之explain的各列含義

標籤：style   blog   http   ar   color   os   sp   on   div   

mysql> explain select customer_id,first_name,last_name from customer;+----+-------------+----------+------+---------------+------+---------+------+------+-------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+------+---------+------+------+-------+| 1 | SIMPLE | customer | ALL | NULL | NULL | NULL | NULL | 599 | NULL |+----+-------------+----------+------+---------------+------+---------+------+------+-------+1 row in set (0.00 sec)

 返回各列的含義
extra列需要注意的傳回值
Using filesort:看到這個的時候，查詢就需要最佳化了
Using temporary 看到這個的時候，也需要最佳化，

http://www.imooc.com/video/3710

筆記

 

mysql> explain select max(payment_date) from payment\G*************************** 1. row ***************************           id: 1  select_type: SIMPLE        table: payment         type: ALLpossible_keys: NULL          key: NULL      key_len: NULL          ref: NULL         rows: 16086        Extra: NULL1 row in set (0.00 sec)mysql> 

 

mysql慢查詢最佳化之explain的各列含義