有人可以建议一个好的索引来使此查询更快地运行吗？
SELECT
s.*,
sl.session_id AS session_id,
sl.lesson_id AS lesson_id
FROM
cdu_sessions s
INNER JOIN cdu_sessions_lessons sl ON sl.session_id = s.id
WHERE
(s.sort = '1') AND
(s.enabled = '1') AND
(s.teacher_id IN ('193', '1', '168', '1797', '7622', '19951'))
说明：
id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra
1 | SIMPLE | s | NULL | ALL | PRIMARY | NULL | NULL | NULL | 2993 | 0.50 | Using where
1 | SIMPLE | sl | NULL | ref | session_id,ix2 | ix2 | 4 | ealteach_main.s.id | 5 | 100.00 | Using index
cdu_sessions看起来像这样：
------------------------------------------------
id | int(11)
name | varchar(255)
map_location | enum('classroom', 'school'...)
sort | tinyint(1)
sort_titles | tinyint(1)
friend_gender | enum('boy', 'girl'...)
friend_name | varchar(255)
friend_description | varchar(2048)
friend_description_format | varchar(128)
friend_description_audio | varchar(255)
friend_description_audio_fid | int(11)
enabled | tinyint(1)
created | int(11)
teacher_id | int(11)
custom | int(1)
------------------------------------------------
cdu_sessions_lessons包含3个字段-id，session_id和lesson_id
谢谢！
答案 0 :(得分：2)
如果不查看查询计划，每个表的行数和分布，很难预测一个好的索引以使其运行更快。
但是，我想这可能会有所帮助：
> INFO: Deployment of web application archive C:\Users\e4560\Desktop\address-manager\application\target\apache-tomee\webapps\ROOT.war has finished in 12,030 ms
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8080"]
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-bio-8009"]
Jan 18, 2019 10:31:57 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 12240 ms
Jan 18, 2019 10:31:57 AM org.apache.catalina.core.StandardServer await
SEVERE: StandardServer.await: create[localhost:8005]:
java.net.BindException: Address already in use: JVM_Bind
at java.net.DualStackPlainSocketImpl.bind0(Native Method)
at java.net.DualStackPlainSocketImpl.socketBind(DualStackPlainSocketImpl.java:106)
at java.net.AbstractPlainSocketImpl.bind(AbstractPlainSocketImpl.java:387)
at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:190)
at java.net.ServerSocket.bind(ServerSocket.java:375)
at java.net.ServerSocket.<init>(ServerSocket.java:237)
at org.apache.catalina.core.StandardServer.await(StandardServer.java:444)
at org.apache.catalina.startup.Catalina.await(Catalina.java:782)
at org.apache.catalina.startup.Catalina.start(Catalina.java:728)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:428)
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["http-bio-8080"]
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["ajp-bio-8009"]
Jan 18, 2019 10:31:57 AM org.apache.catalina.core.StandardService stopInternal
INFO: Stopping service Catalina
Jan 18, 2019 10:31:57 AM org.apache.openejb.assembler.classic.Assembler destroyApplication
INFO: Undeploying app: C:\Users\e09340\Desktop\address-manager\application\target\apache-tomee\webapps\ROOT
Jan 18, 2019 10:31:57 AM org.apache.openejb.util.OptionsLog info
INFO: Using 'openjpa.Log=org.apache.openejb.openjpa.JULOpenJPALogFactory'
Jan 18, 2019 10:31:57 AM org.apache.openejb.assembler.classic.Assembler destroyApplication
INFO: Undeployed app: C:\Users\epom\Desktop\address-manager\application\target\apache-tomee\webapps\ROOT
Jan 18, 2019 10:31:57 AM org.apache.catalina.loader.WebappClassLoaderBase checkThreadLocalMapForLeaks
SEVERE: The web application [] created a ThreadLocal with key of type [com.netflix.hystrix.Hystrix$1] (value [com.netflix.hystrix.Hystrix$1@4eedec61]) and a value of type [com.netflix.hystrix.Hystrix.ConcurrentStack] (value [com.netflix.hystrix.Hystrix$ConcurrentStack@740a0cb2]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol stop
INFO: Stopping ProtocolHandler ["http-bio-8080"]
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol stop
INFO: Stopping ProtocolHandler ["ajp-bio-8009"]
Jan 18, 2019 10:31:57 AM org.apache.openejb.server.SimpleServiceManager stop
INFO: Stopping server services
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["http-bio-8080"]
Jan 18, 2019 10:31:57 AM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["ajp-bio-8009"]
答案 1 :(得分：1)
查看可以在哪里使用表cdu_sessions的复合索引
create index idx1 on cdu_sessions(teacher_id, sort, enabled);
并希望加入并选择表cdu_sessions_lessons
create index idx2 on cdu_sessions_lessons(session_id, lesson_id);
答案 2 :(得分：0)
首先，编写查询，因此不需要类型转换。 where子句中的所有比较都是对数字的比较，因此请使用数字常量：
SELECT s.*,
sl.session_id, -- unnecessary because s.id is in the result set
sl.lesson_id
FROM cdu_sessions s INNER JOIN
cdu_sessions_lessons sl
ON sl.session_id = s.id
WHERE s.sort = 1 AND
s.enabled = 1 AND
s.teacher_id IN (193, 1, 168, 1797, 7622, 19951);
尽管在这种特定情况下可能不会发生，但是混合类型会阻碍索引的使用。
我删除了该列作为别名（例如as session_id）。这些都是多余的，因为列名是别名，并且查询没有更改名称。
对于此查询，请首先查看WHERE子句。所有列引用均来自一张表。这些应该放在索引中，首先进行相等比较：
create index idx_cdu_sessions_4 on cdu_sessions(sort, enabled, teacher_id, id)
我添加了id，因为它也用在JOIN中。
正式地，如果索引id是主键，则它是不需要的。但是，如果我想要在那里，我喜欢明确表达。
接下来，您要为第二张表建立索引。从那里仅引用两列，因此它们都可以进入索引。第一列应该是join中使用的列：
create index idx_cdu_sessions_lessons_2 on cdu_sessions_lessons(session_id, lesson_id);