Sending data select * from `rep_corp_vehicle_online_count` where corp_id = 48 and vehicle_id = 10017543

mysql> desc rep_corp_vehicle_online_count;
+-------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| corp_id | int(11) | NO | | NULL | |
| vehicle_id | int(11) | NO | | NULL | |
| online_day | varchar(20) | NO | | NULL | |
| loc_total | int(11) | NO | | NULL | |
| create_time | datetime | NO | | NULL | |
| update_time | datetime | NO | | NULL | |
+-------------+-------------+------+-----+---------+----------------+
7 rows in set (0.00 sec) 

mysql> show index from rep_corp_vehicle_online_count;
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| rep_corp_vehicle_online_count | 0 | PRIMARY | 1 | id | A | 1247259 | NULL | NULL | | BTREE | | |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec) 

mysql>explain select * from rep_corp_vehicle_online_count where corp_id = 79 and vehicle_id = 10016911 and online_day = '2016-03-29'\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: rep_corp_vehicle_online_count
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 1248495
Extra: Using where
1 row in set (0.00 sec) 

mysql> select count(distinct corp_id) from rep_corp_vehicle_online_count;
+-------------------------+
| count(distinct corp_id) |
+-------------------------+
| 18 |
+-------------------------+
1 row in set (0.63 sec)
mysql> select count(corp_id) from rep_corp_vehicle_online_count; 
+----------------+
| count(corp_id) |
+----------------+
| 1239573 |
+----------------+
1 row in set (0.00 sec)
mysql> select count(distinct vehicle_id) from rep_corp_vehicle_online_count; 
+----------------------------+
| count(distinct vehicle_id) |
+----------------------------+
| 2580 |
+----------------------------+
1 row in set (1.03 sec)
mysql>explain select count(vehicle_id) from rep_corp_vehicle_online_count; 
+-------------------+
| count(vehicle_id) |
+-------------------+
| 1239911 |
+-------------------+
1 row in set (0.00 sec) 

mysql> create index r_c_v on rep_corp_vehicle_online_count(corp_id,vehicle_id); 
Query OK, 1487993 rows affected (6.09 sec)
Records: 1487993 Duplicates: 0 Warnings: 0
mysql> show index from rep_corp_vehicle_online_count;
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| rep_corp_vehicle_online_count | 0 | PRIMARY | 1 | id | A | 1490176 | NULL | NULL | | BTREE | | |
| rep_corp_vehicle_online_count | 1 | r_c_v | 1 | corp_id | A | 18 | NULL | NULL | | BTREE | | |
| rep_corp_vehicle_online_count | 1 | r_c_v | 2 | vehicle_id | A | 2596 | NULL | NULL | | BTREE | | |
+-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)