lle*_*eto 5 mysql indexing performance
我有一个 MySQL 表，其中包含大约 2000 万行数据。
+-------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| b_id | int(11) | YES | MUL | NULL | |
| order | bigint(20) | YES | MUL | NULL | |
| date | date | YES | | NULL | |
| time | time | YES | | NULL | |
| channel | varchar(8) | YES | MUL | NULL | |
| data | varchar(60) | YES | | NULL | |
| date_system | date | YES | MUL | NULL | |
| time_system | time | YES | | NULL | |
+-------------+-------------+------+-----+---------+----------------+
我在（b_id，频道，日期）上有一个非唯一索引，以加快查询速度，例如：
select date, left(time,2) as hour, round(data,1) as data
from data_lines
where channel='1'
and b_id='300'
and date >='2013-04-19'
and date <='2013-04-26'
group by date,hour
问题是我的插入有时会重叠，所以我想使用“ON DUPLICATE KEY UPDATE”，但这需要一个唯一的索引。因此，我在 (b_id、channel、date、time) 上创建了一个唯一索引，因为这是确定是否存在 double 值的四个主要特征。现在插入工作正常，但是我的选择查询速度慢得令人无法接受。
我不太确定为什么自从添加新索引以来我的选择变得更慢：
对于记录（order、date_system 和 time_system），在索引或选择中根本不使用，但包含数据。插入由 C 和 Python 运行，选择由 PHP 运行。
根据请求解释查询：
mysql> explain select date, left(time,2) as hour, round(data,1) as data
from data_lines
where channel='1'
and b_id='300'
and date >='2013-04-19'
and date <='2013-04-26'
group by date,hour;
+----+-------------+-----------+------+--------------------------------+------------+---------+-------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------+------+--------------------------------+------------+---------+-------------+------+----------------------------------------------+
| 1 | SIMPLE | data_lines| ref | update_index,b_id,comp_index | comp_index | 16 | const,const | 3548 | Using where; Using temporary; Using filesort |
+----+-------------+-----------+------+--------------------------------+------------+---------+-------------+------+----------------------------------------------+
update_index 是我的（b_id，频道，日期，时间）的唯一索引，comp_index 是我的（b_id，频道，日期）的非唯一索引。
索引为：
+-----------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| data_lines| 0 | PRIMARY | 1 | id | A | 17918898 | NULL | NULL | | BTREE | | |
| data_lines| 0 | id_UNIQUE | 1 | id | A | 17918898 | NULL | NULL | | BTREE | | |
| data_lines| 0 | update_index | 1 | channel | A | 17 | NULL | NULL | YES | BTREE | | |
| data_lines| 0 | update_index | 2 | b_id | A | 17 | NULL | NULL | YES | BTREE | | |
| data_lines| 0 | update_index | 3 | date | A | 44244 | NULL | NULL | YES | BTREE | | |
| data_lines| 0 | update_index | 4 | time | A | 17918898 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | box_id | 1 | b_id | A | 17 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | idx | 1 | order | A | 17918898 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | comp_index | 1 | b_id | A | 17 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | comp_index | 2 | channel | A | 6624 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | comp_index | 3 | date | A | 165915 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | date_system | 1 | date_system | A | 17 | NULL | NULL | YES | BTREE | | |
| data_lines| 1 | mac | 1 | mac | A | 17 | NULL | NULL | YES | BTREE | | |
+-----------+------------+--------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+