mysql - 为什么同一个查询可能需要 1000 倍的时间，具体取决于 where 子句？

Question

我有一个相当大的查询，它使用连接在多个表中收集大量信息。该数据库是来自城市公共(public)交通系统的GTFS公交信息。

我使用不同的 WHERE 子句运行相同的查询，所用时间可能从 200 毫秒到 200 秒不等。

如果您不需要解释，请直接向下滚动到问题。

数据库

表格是:

• 路线
• trips:使用route_id
连接到routes
• stop_times:连接到tripsusingtrip_id`
• stops:使用 stop_id
连接到 stop_times
• stop_connections:连接两个stop_id

我的目标是选择使用 2 个连接的旅程。这是我的查询在纸上的样子:

解释:

• 黑色信息是表格，每行一种表格类型(即第一行是trips 表格)。
• 红色信息是我查询中的别名(s是stops，st是stop_times，t为trips，a为到达，d为出发，1/2/3为行程索引)
• 绿色信息是每张表的条件列表

基本上是:

1. [s1d ] 从给定的 stop_id 开始
2. [st1d] 获取从该站点出发的行程的出发时间
3. [t1 ] 将这些行程限制在我们想要的 route_id 集合
4. [st1a] 获取站点到达时间
5. [s1a ] 获取站点信息(站点名称)
6. [cs1 ] 将此站点连接到步行距离内的所有其他站点

重复此操作 3 次，得到 3 趟(2 次连接)，并将到达站过滤为我想要的。

查询

select 

    s1d.stop_id as s1d_id, s1d.stop_name as s1d_name, s1d.stop_lat as s1d_lat, s1d.stop_lon as s1d_lon, 
    st1d.departure_time as st1d_dep, 
    t1.trip_id as t1_id, t1.trip_headsign as t1_headsign, t1.route_id as t1_route, t1.direction_id as t1_dir, 
    st1a.departure_time as st1a_dep, 
    s1a.stop_id as s1a_id, s1a.stop_name as s1a_name, s1a.stop_lat as s1a_lat, s1a.stop_lon as s1a_lon, 
    cs1.from_stop_id, cs1.to_stop_id, 
    s2d.stop_id as s2d_id, s2d.stop_name as s2d_name, s2d.stop_lat as s2d_lat, s2d.stop_lon as s2d_lon,  
    st2d.departure_time as st2d_dep, 
    t2.trip_id as t2_id, t2.trip_headsign as t2_headsign, t2.route_id as t2_route, t2.direction_id as t2_dir, 
    st2a.departure_time as st2a_dep, 
    s2a.stop_id as s2a_id, s2a.stop_name as s2a_name, s2a.stop_lat as s2a_lat, s2a.stop_lon as s2a_lon, 
    cs2.from_stop_id, cs2.to_stop_id, 
    s3d.stop_id as s3d_id, s3d.stop_name as s3d_name, s3d.stop_lat as s3d_lat, s3d.stop_lon as s3d_lon,  
    st3d.departure_time as st3d_dep, 
    t3.trip_id as t3_id, t3.trip_headsign as t3_headsign, t3.route_id as t3_route, t3.direction_id as t3_dir, 
    st3a.departure_time as st3a_dep, 
    s3a.stop_id as s3a_id, s3a.stop_name as s3a_name, s3a.stop_lat as s3a_lat, s3a.stop_lon as s3a_lon

from stops s1d

left join stop_times st1d on st1d.stop_id = s1d.stop_id     
    and st1d.departure_time > '07:33:00' and st1d.departure_time < '08:33:00'

left join trips t1 on t1.trip_id = st1d.trip_id     
    and t1.service_id in (select service_id from calendar where start_date <= 20141020 and end_date >= 20141020 and monday = 1) 
    and t1.route_id in ('11-0') 

left join stop_times st1a on st1a.trip_id = t1.trip_id      
    and st1a.departure_time > st1d.departure_time

left join stops s1a on s1a.stop_id = st1a.stop_id 

left join stop_connections cs1 on cs1.from_stop_id = st1a.stop_id 

left join stops s2d on s2d.stop_id = cs1.to_stop_id 

left join stop_times st2d on st2d.stop_id = s2d.stop_id 
    and st2d.departure_time > addtime(st1a.departure_time, '00:03:00')
    and st2d.departure_time < addtime(st1a.departure_time, '01:03:00')

left join trips t2 on t2.trip_id = st2d.trip_id     
    and t2.service_id in (select service_id from calendar where start_date <= 20141020 and end_date >= 20141020 and monday = 1) 
    and t2.route_id in ('3-0', 'NA-0', '4-0', '2-0') 

left join stop_times st2a on st2a.trip_id = t2.trip_id and st2a.departure_time > st2d.departure_time 

left join stops s2a on s2a.stop_id = st2a.stop_id 

left join stop_connections cs2 on cs2.from_stop_id = st2a.stop_id 

left join stops s3d on s3d.stop_id = cs2.to_stop_id 

left join stop_times st3d on st3d.stop_id = s3d.stop_id         
    and st3d.departure_time > addtime(st2a.departure_time, '00:03:00')
    and st3d.departure_time < addtime(st2a.departure_time, '01:03:00')

left join trips t3 on t3.trip_id = st3d.trip_id 
    and t3.service_id in (select service_id from calendar where start_date <= 20141020 and end_date >= 20141020 and monday = 1) 
    and t3.route_id in ('36-0', '30-0', '97-0')
    left join stop_times st3a on st3a.trip_id = t3.trip_id 

    and st3a.departure_time > st3d.departure_time 

    and st3a.stop_id in ('StopPoint:CLBO2',
     'StopArea:CLBO',
     'StopPoint:CLBO1',
     'StopPoint:PLTI2',
     'StopPoint:LCBU2',
     'StopArea:LCBU',
     'StopPoint:LCBU1',
     'StopPoint:MHDI2',
     'StopPoint:BILE2',
     'StopArea:MHDI',
     'StopPoint:MHDI1',
     'StopPoint:MREZ2',
     'StopArea:MRDI',
     'StopPoint:MRDI1',
     'StopArea:SORI',
     'StopPoint:SORI1',
     'StopArea:MREZ',
     'StopPoint:MREZ1',
     'StopPoint:SORI2',
     'StopArea:BILE',
     'StopPoint:BILE1',
     'StopPoint:MRDI2',
     'StopArea:PLTI',
     'StopPoint:PLTI1',
     'StopPoint:SEIL3',
     'StopPoint:SEIL2',
     'StopArea:SEIL',
     'StopPoint:SEIL1')
    left join stops s3a on s3a.stop_id = st3a.stop_id

where s1d.stop_id = 'StopPoint:DEMO1'

group by s1d_id, s3a_id
having s3a_id is not null
order by s1d_id asc, st1d_dep asc, st1a_dep asc, s1a_id asc, s2d_id asc, st2d_dep asc, st2a_dep asc, s2a_id asc, s3d_id asc, st3d_dep asc, st3a_dep asc, s3a_id asc

问题

我运行这个查询两次，唯一的区别是最后的 where 子句:

• 其中 s1d.stop_id = 'StopPoint:DEMO1':集合中有 13 行(2 分 58.81 秒)
• 其中 s1d.stop_id = 'StopPoint:ECTE2':空集(0.25 秒)

这对我来说很奇怪。以下是对这两个查询的解释:

从 DEMO1 出发(13 个结果，缓慢)

使用 EXPLAIN SELECT...:

+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+-------------+
| id | select_type | table    | type   | possible_keys                             | key              | key_len | ref                              | rows | Extra       |
+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+-------------+
|  1 | SIMPLE      | s1d      | ALL    | NULL                                      | NULL             | NULL    | NULL                             | 3411 | NULL        |
|  1 | SIMPLE      | st1d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s1d.stop_id    |  163 | Using where |
|  1 | SIMPLE      | t1       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st1d.trip_id   |    1 | Using where |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t1.service_id  |    1 | Using where |
|  1 | SIMPLE      | st1a     | ref    | st_trip_id_idx                            | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t1.trip_id     |   14 | Using where |
|  1 | SIMPLE      | s1a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st1a.stop_id   |    1 | NULL        |
|  1 | SIMPLE      | cs1      | ref    | from_to_stop_ids                          | from_to_stop_ids | 302     | bicou_gtfs_nantes.st1a.stop_id   |    1 | Using index |
|  1 | SIMPLE      | s2d      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.cs1.to_stop_id |    1 | NULL        |
|  1 | SIMPLE      | st2d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s2d.stop_id    |  163 | Using where |
|  1 | SIMPLE      | t2       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st2d.trip_id   |    1 | Using where |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t2.service_id  |    1 | Using where |
|  1 | SIMPLE      | st2a     | ref    | st_trip_id_idx                            | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t2.trip_id     |   14 | Using where |
|  1 | SIMPLE      | s2a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st2a.stop_id   |    1 | NULL        |
|  1 | SIMPLE      | cs2      | ref    | from_to_stop_ids                          | from_to_stop_ids | 302     | bicou_gtfs_nantes.st2a.stop_id   |    1 | Using index |
|  1 | SIMPLE      | s3d      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.cs2.to_stop_id |    1 | NULL        |
|  1 | SIMPLE      | st3d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s3d.stop_id    |  163 | Using where |
|  1 | SIMPLE      | t3       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st3d.trip_id   |    1 | Using where |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t3.service_id  |    1 | Using where |
|  1 | SIMPLE      | st3a     | ref    | st_stop_id_idx,st_trip_id_idx             | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t3.trip_id     |   14 | Using where |
|  1 | SIMPLE      | s3a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st3a.stop_id   |    1 | NULL        |
+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+-------------+

使用 EXPLAIN EXTENDED...:

+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+----------+---------------------------------+
| id | select_type | table    | type   | possible_keys                             | key              | key_len | ref                              | rows | filtered | Extra                           |
+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+----------+---------------------------------+
|  1 | SIMPLE      | s1d      | const  | PRIMARY                                   | PRIMARY          | 302     | const                            |    1 |   100.00 | Using temporary; Using filesort |
|  1 | SIMPLE      | st1d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | const                            |  234 |   100.00 | Using where                     |
|  1 | SIMPLE      | t1       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st1d.trip_id   |    1 |   100.00 | Using where                     |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t1.service_id  |    1 |   100.00 | Using where                     |
|  1 | SIMPLE      | st1a     | ref    | st_trip_id_idx                            | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t1.trip_id     |   14 |   100.00 | Using where                     |
|  1 | SIMPLE      | s1a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st1a.stop_id   |    1 |   100.00 | NULL                            |
|  1 | SIMPLE      | cs1      | ref    | from_to_stop_ids                          | from_to_stop_ids | 302     | bicou_gtfs_nantes.st1a.stop_id   |    1 |   100.00 | Using index                     |
|  1 | SIMPLE      | s2d      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.cs1.to_stop_id |    1 |   100.00 | NULL                            |
|  1 | SIMPLE      | st2d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s2d.stop_id    |  163 |   100.00 | Using where                     |
|  1 | SIMPLE      | t2       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st2d.trip_id   |    1 |   100.00 | Using where                     |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t2.service_id  |    1 |   100.00 | Using where                     |
|  1 | SIMPLE      | st2a     | ref    | st_trip_id_idx                            | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t2.trip_id     |   14 |   100.00 | Using where                     |
|  1 | SIMPLE      | s2a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st2a.stop_id   |    1 |   100.00 | NULL                            |
|  1 | SIMPLE      | cs2      | ref    | from_to_stop_ids                          | from_to_stop_ids | 302     | bicou_gtfs_nantes.st2a.stop_id   |    1 |   100.00 | Using index                     |
|  1 | SIMPLE      | s3d      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.cs2.to_stop_id |    1 |   100.00 | NULL                            |
|  1 | SIMPLE      | st3d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s3d.stop_id    |  163 |   100.00 | Using where                     |
|  1 | SIMPLE      | t3       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st3d.trip_id   |    1 |   100.00 | Using where                     |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t3.service_id  |    1 |   100.00 | Using where                     |
|  1 | SIMPLE      | st3a     | ref    | st_stop_id_idx,st_trip_id_idx             | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t3.trip_id     |   14 |   100.00 | Using where                     |
|  1 | SIMPLE      | s3a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st3a.stop_id   |    1 |   100.00 | NULL                            |
+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+----------+---------------------------------+

从 ECTE2 出发(0 结果，快)

+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+---------------------------------+
| id | select_type | table    | type   | possible_keys                             | key              | key_len | ref                              | rows | Extra                           |
+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+---------------------------------+
|  1 | SIMPLE      | s1d      | const  | PRIMARY                                   | PRIMARY          | 302     | const                            |    1 | Using temporary; Using filesort |
|  1 | SIMPLE      | st1d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | const                            |  234 | Using where                     |
|  1 | SIMPLE      | t1       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st1d.trip_id   |    1 | Using where                     |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t1.service_id  |    1 | Using where                     |
|  1 | SIMPLE      | st1a     | ref    | st_trip_id_idx                            | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t1.trip_id     |   14 | Using where                     |
|  1 | SIMPLE      | s1a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st1a.stop_id   |    1 | NULL                            |
|  1 | SIMPLE      | cs1      | ref    | from_to_stop_ids                          | from_to_stop_ids | 302     | bicou_gtfs_nantes.st1a.stop_id   |    1 | Using index                     |
|  1 | SIMPLE      | s2d      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.cs1.to_stop_id |    1 | NULL                            |
|  1 | SIMPLE      | st2d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s2d.stop_id    |  163 | Using where                     |
|  1 | SIMPLE      | t2       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st2d.trip_id   |    1 | Using where                     |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t2.service_id  |    1 | Using where                     |
|  1 | SIMPLE      | st2a     | ref    | st_trip_id_idx                            | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t2.trip_id     |   14 | Using where                     |
|  1 | SIMPLE      | s2a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st2a.stop_id   |    1 | NULL                            |
|  1 | SIMPLE      | cs2      | ref    | from_to_stop_ids                          | from_to_stop_ids | 302     | bicou_gtfs_nantes.st2a.stop_id   |    1 | Using index                     |
|  1 | SIMPLE      | s3d      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.cs2.to_stop_id |    1 | NULL                            |
|  1 | SIMPLE      | st3d     | ref    | st_stop_id_idx                            | st_stop_id_idx   | 302     | bicou_gtfs_nantes.s3d.stop_id    |  163 | Using where                     |
|  1 | SIMPLE      | t3       | eq_ref | PRIMARY,trip_service_id,trip_route_id_idx | PRIMARY          | 302     | bicou_gtfs_nantes.st3d.trip_id   |    1 | Using where                     |
|  1 | SIMPLE      | calendar | eq_ref | PRIMARY,service_id                        | PRIMARY          | 302     | bicou_gtfs_nantes.t3.service_id  |    1 | Using where                     |
|  1 | SIMPLE      | st3a     | ref    | st_stop_id_idx,st_trip_id_idx             | st_trip_id_idx   | 302     | bicou_gtfs_nantes.t3.trip_id     |   14 | Using where                     |
|  1 | SIMPLE      | s3a      | eq_ref | PRIMARY                                   | PRIMARY          | 302     | bicou_gtfs_nantes.st3a.stop_id   |    1 | NULL                            |
+----+-------------+----------+--------+-------------------------------------------+------------------+---------+----------------------------------+------+---------------------------------+

显然引擎以不同的方式处理这两个查询。现在为什么是另一个问题。

s1d 对象来自表stops:

CREATE TABLE IF NOT EXISTS `stops` (
  `stop_id` VARCHAR(100) NOT NULL,
  `stop_code` VARCHAR(50) NULL DEFAULT NULL,
  `stop_name` VARCHAR(255) NOT NULL,
  `stop_desc` VARCHAR(255) NULL DEFAULT NULL,
  `stop_lat` DECIMAL(10,6) NOT NULL,
  `stop_lon` DECIMAL(10,6) NOT NULL,
  `zone_id` VARCHAR(255) NULL DEFAULT NULL,
  `stop_url` VARCHAR(255) NULL DEFAULT NULL,
  `location_type` VARCHAR(2) NULL DEFAULT NULL,
  `parent_station` VARCHAR(100) NOT NULL,
  `stop_timezone` VARCHAR(50) NULL DEFAULT NULL,
  `wheelchair_boarding` TINYINT(1) NULL DEFAULT NULL,
  PRIMARY KEY (`stop_id`),
  INDEX `zone_id` (`zone_id` ASC),
  INDEX `stop_lat` (`stop_lat` ASC),
  INDEX `stop_lon` (`stop_lon` ASC),
  INDEX `location_type` (`location_type` ASC),
  INDEX `parent_station` (`parent_station` ASC),
  CONSTRAINT `stop_parent_station`
    FOREIGN KEY (`parent_station`)
    REFERENCES `stops` (`stop_id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8

我不明白为什么在没有数据时引擎会正确使用索引和键；当有数据(13 行)时，引擎不使用索引和键，而是浏览 3000 行而不是 1 行。

我有什么办法可以强制引擎在特定表上使用键吗？
另外，为什么引擎会这样？

环境:

• 操作系统:Mac OS X 10.10
• SQL 客户端:mysql Ver 14.14 Distrib 5.6.17，适用于 osx10.6 (i386)，使用 EditLine 包装器
• SQL 服务器:5.6.21 MySQL 社区服务器 (GPL)
• 硬件:MacBook Air、Intel Core i7、8GB RAM、256GB SSD(应该很快)

表格大小:

+-------------------+------------+
| table_name        | TABLE_ROWS |
+-------------------+------------+
| agency            |          0 |
| calendar          |         28 |
| calendar_dates    |       1005 |
| fare_attributes   |          0 |
| fare_rules        |          0 |
| feed_info         |          0 |
| frequencies       |          0 |
| route_connections |      20919 |
| routes            |         60 |
| shapes            |          0 |
| stop_connections  |      11617 |
| stop_times        |     768682 |
| stops             |       3411 |
| stops_routes      |      16652 |
| transfers         |          0 |
| trips             |      31913 |
+-------------------+------------+

每个连接表后的行数:

+---------+-------------+------------+
| Table   |  DEMO1      |   ECTE2    |
+---------+-------------+------------+
| s1d     |           1 |          1 |
| st1d    |          16 |         18 |
| t1      |          16 |         18 |
| st1a    |         271 |        117 |
| s1a     |         271 |        117 |
| cs1     |        1286 |        495 |
| s1d     |        1286 |        495 |
| st2d    |       32958 |       5973 |
| t2      |       32958 |       5973 |
| st2a    |       65891 |       5973 |
| s2a     |       65891 |       5973 |
| cs2     |      206455 |       5973 |
| s3d     |      206455 |       5973 |
| st3d    |     4284871 |       5973 |
| t3      |     4284871 |       5973 |
| st3a    |     4351249 |       5973 |
| s3a     |     4351249 |       5973 |
| +having |          13 |          0 |
+---------+-------------+------------+

Answer 1

我想到了两个想法:

1) 将一些索引切换为BTEE 索引。默认值是 HASH，它适用于相等/不相等比较，而不是 IN(...)。参见 here

2) 查看优化器对您的查询做了什么。做一个

EXPLAIN EXTENDED SELECT ...

关于这两个查询。这会给你一个包含查询优化器输出的警告。您应该在这里看到不同之处。