mysql慢查询优化之explain的各列含义

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)

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

mysql>