Finology 大数据金融

通过大数据以量化金融

发表于 更新于 分类于 阅读次数： Waline：

对于这个充分和必要条件，现在梳理一下。

如果 A => B 且 A </= B，即如果 A 能推出 B，且 B 不能推出 A，则 A 是 B 的充分（不必要）条件。

如果 A =/> B 且 A <= B，即如果 A 不能推出 B，且 B 能推出 A，则 A 是 B 的必要（不充分）条件。

可微条件

必要条件

即可微，能推出什么。

若函数在某点可微分，则函数在该点必连续；

若二元函数在某点可微分，则该函数在该点对x和y的偏导数必存在。

充分条件

即什么能推出可微。

若函数对x和y的偏导数在这点的某一邻域内都存在，且均在这点连续，则该函数在这点可微。

发表于 更新于 分类于 ， 阅读次数： Waline：

单列去重比较简单，如果多列要去重，怎么找出重复的值？

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SELECT 
    field1, COUNT(field1),
    field2, COUNT(field2),
    ...

FROM
    table_name
GROUP BY
    field1, 
    field2,
    ...
HAVING 
    (COUNT(field1) > 1) AND 
    (COUNT(field2) > 1) AND 
     ...

发表于 更新于 分类于 ， 阅读次数： Waline：

Spring boot 项目中，集成了 RabbitMQ。但有时候，做测试的时候，可能 RabbitMQ 并未启动，这时就会导致项目启动时间很长，还会报如下错误信息：

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020-05-05 18:00:22.267 ERROR 78855 --- [           main] o.s.a.r.l.SimpleMessageListenerContainer : Consumer failed to start in 60000 milliseconds; does the task executor have enough threads to support the container concurrency?
2020-05-05 18:00:22.305 ERROR 78855 --- [ntContainer#0-2] o.s.a.r.l.SimpleMessageListenerContainer : Failed to check/redeclare auto-delete queue(s).

org.springframework.amqp.AmqpIOException: java.net.SocketTimeoutException: connect timed out
	at org.springframework.amqp.rabbit.support.RabbitExceptionTranslator.convertRabbitAccessException(RabbitExceptionTranslator.java:70) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.connection.AbstractConnectionFactory.createBareConnection(AbstractConnectionFactory.java:510) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.connection.CachingConnectionFactory.createConnection(CachingConnectionFactory.java:751) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.connection.ConnectionFactoryUtils.createConnection(ConnectionFactoryUtils.java:214) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.core.RabbitTemplate.doExecute(RabbitTemplate.java:2095) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.core.RabbitTemplate.execute(RabbitTemplate.java:2068) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.core.RabbitTemplate.execute(RabbitTemplate.java:2048) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.core.RabbitAdmin.getQueueInfo(RabbitAdmin.java:407) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.core.RabbitAdmin.getQueueProperties(RabbitAdmin.java:391) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.attemptDeclarations(AbstractMessageListenerContainer.java:1830) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.redeclareElementsIfNecessary(AbstractMessageListenerContainer.java:1811) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.initialize(SimpleMessageListenerContainer.java:1342) [spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.run(SimpleMessageListenerContainer.java:1188) [spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at java.lang.Thread.run(Thread.java:745) [na:1.8.0_92]
Caused by: java.net.SocketTimeoutException: connect timed out
	at java.net.PlainSocketImpl.socketConnect(Native Method) ~[na:1.8.0_92]
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_92]
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_92]
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_92]
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_92]
	at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_92]
	at com.rabbitmq.client.impl.SocketFrameHandlerFactory.create(SocketFrameHandlerFactory.java:60) ~[amqp-client-5.7.3.jar:5.7.3]
	at com.rabbitmq.client.ConnectionFactory.newConnection(ConnectionFactory.java:1113) ~[amqp-client-5.7.3.jar:5.7.3]
	at com.rabbitmq.client.ConnectionFactory.newConnection(ConnectionFactory.java:1063) ~[amqp-client-5.7.3.jar:5.7.3]
	at org.springframework.amqp.rabbit.connection.AbstractConnectionFactory.connect(AbstractConnectionFactory.java:526) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	at org.springframework.amqp.rabbit.connection.AbstractConnectionFactory.createBareConnection(AbstractConnectionFactory.java:473) ~[spring-rabbit-2.2.5.RELEASE.jar:2.2.5.RELEASE]
	... 12 common frames omitted

如何不启动 RabbitMQ 呢？

我们只需要在启动类或者是测试启动类上添加如下注解：

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@EnableAutoConfiguration(exclude = {RabbitAutoConfiguration.class})

同时在注入了 RabbitTemplate 的类上面添加如下注解：

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@Profile("no_rabbit")

no_rabbit 任意写，只要不是我们启动类的 Profile 就可以了。

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