Question

我有一个表t1的postgresql数据库，我想计算一个阈值。阈值应该是例如汽车1使用的燃料比所有汽车的75％多，car2使用的燃料比所有汽车的50％多，.... 在数学上我理解我想做什么，但我不知道如何构建查询

id | name | value | threshold
________________________

1  | car1 |  30   |  ...%
2  | car2 |  15   |  ..%
3  | car3 |   7   |
4  | car4 |   5   |

这是一个sql小提琴 http://sqlfiddle.com/#!15/1e914/1

UPDATE t1
SET threshold = 
    select count(value)
     from t1

其中（值＆gt; [每行]）然后是* 100 /总计数（）

抱歉这个糟糕的尝试，但我有点迷茫。还尝试了一些集合函数。

Answer 1

您可以使用window function：

非常优雅地解决这个问题

UPDATE t1
SET threshold = sub.thr
FROM (
  SELECT id, 100. * (rank() OVER (ORDER BY value) - 1) / count(*) OVER () AS thr
  FROM t1) sub
WHERE t1.id = sub.id;

rank()函数给出有序集中的排名（从1开始），在本例中为value列，然后除以集合中的总行数。请注意，count(*) OVER ()计算分区中的总行数，但它不像常规count(*)那样聚合行。

Answer 2

WITH    q AS
        (
        SELECT  *,
                (RANK() OVER (ORDER BY value) - 1) * 100. / COUNT(*) OVER () nt
        FROM mytable
        )
UPDATE  mytable
SET     threshold = nt
FROM    q
WHERE   mytable.id = q.id

Answer 3

您想计算使用燃料的百分比吗？

<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
    xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany.cbp.dv</groupId>
  <artifactId>demo-cbp-dv</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <name>demo app </name>
  <url>http://www.demhas.com</url>
  <packaging>bundle</packaging>
  <properties>

    <fabric8.profile>demhas-cbp-dv</fabric8.profile>

    <fabric8.features>feature-camel</fabric8.features>
    <fabric8.bundles>wrap:mvn:com.oracle/ojdbc6/${ojdbc-version}
                    wrap:mvn:commons-dbcp/commons-dbcp/${commons-dbcp-version}
                    wrap:mvn:org.json/json/${json-version}
    </fabric8.bundles>


    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <activemq-version>5.10.0</activemq-version>
    <jackson-version>2.5.4</jackson-version>
    <json-version>20150729</json-version>
    <json2-version>20140107</json2-version>
    <slf4j-version>1.7.12</slf4j-version>
    <log4j-version>1.2.17</log4j-version>
    <ojdbc-version>11.2.0.4</ojdbc-version>
    <commons-dbcp-version>1.4</commons-dbcp-version>
    <camel-version>2.15.2</camel-version>

    <fabic8-version>1.2.0.redhat-133</fabic8-version>

  </properties>

  <dependencies>
      <dependency>
        <groupId>org.ow2.asm</groupId>
        <artifactId>asm-commons</artifactId>
        <version>4.1</version>
        <scope>runtime</scope>
    </dependency>

    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-core</artifactId>
      <version>${camel-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-blueprint</artifactId>
      <version>${camel-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-salesforce</artifactId>
      <version>${camel-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-http</artifactId>
      <version>${camel-version}</version>
    </dependency>

    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-jsonpath</artifactId>
      <version>${camel-version}</version>
    </dependency>

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>${slf4j-version}</version>
    </dependency>

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>${slf4j-version}</version>
    </dependency>

    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>${log4j-version}</version>
    </dependency>

    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-mybatis</artifactId>
      <version>${camel-version}</version>
    </dependency>

    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-test-blueprint</artifactId>
      <version>${camel-version}</version>
      <scope>test</scope>
    </dependency>

    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-test</artifactId>
      <version>${camel-version}</version>
      <scope>test</scope>
    </dependency>

    <dependency>
        <groupId>org.apache.camel</groupId>
        <artifactId>camel-jackson</artifactId>
        <version>${camel-version}</version>
    </dependency>    

    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-jaxb</artifactId>
      <version>${camel-version}</version>
    </dependency>

        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc6</artifactId>
            <version>${ojdbc-version}</version>
        </dependency>
    <dependency>
      <groupId>commons-dbcp</groupId>
      <artifactId>commons-dbcp</artifactId>
      <version>${commons-dbcp-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.activemq</groupId>
      <artifactId>activemq-client</artifactId>
      <version>${activemq-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.activemq</groupId>
      <artifactId>activemq-camel</artifactId>
      <version>${activemq-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.activemq</groupId>
      <artifactId>activemq-pool</artifactId>
      <version>${activemq-version} </version>
       <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>${json-version}</version>
    </dependency>
  </dependencies>
  <repositories>
    <repository>
      <releases>
        <enabled>true</enabled>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>public.fusesource.org</id>
      <name>FuseSource Public Repository</name>
      <url>http://repo.fusesource.com/nexus/content/groups/public/</url>
    </repository>
    <repository>
      <releases>
        <enabled>true</enabled>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>release.fusesource.org</id>
      <name>FuseSource Release Repository</name>
      <url>http://repo.fusesource.com/nexus/content/repositories/releases</url>
    </repository>
    <repository>
      <releases>
        <enabled>true</enabled>
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      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>ea.fusesource.org</id>
      <name>FuseSource Community Early Access Release Repository</name>
      <url>http://repo.fusesource.com/nexus/content/groups/ea</url>
    </repository>
    <repository>
      <releases>
        <enabled>false</enabled>
      </releases>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
      <id>snapshot.fusesource.org</id>
      <name>FuseSource Snapshot Repository</name>
      <url>http://repo.fusesource.com/nexus/content/repositories/snapshots</url>
    </repository>
  </repositories>
  <pluginRepositories>
    <pluginRepository>
      <releases>
        <enabled>true</enabled>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>public.fusesource.org</id>
      <name>FuseSource Public Repository</name>
      <url>http://repo.fusesource.com/nexus/content/groups/public</url>
    </pluginRepository>

    <pluginRepository>
      <releases>
        <enabled>true</enabled>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>release.fusesource.org</id>
      <name>FuseSource Release Repository</name>
      <url>http://repo.fusesource.com/nexus/content/repositories/releases</url>
    </pluginRepository>
    <pluginRepository>
      <releases>
        <enabled>true</enabled>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>ea.fusesource.org</id>
      <name>FuseSource Community Early Access Release Repository</name>
      <url>http://repo.fusesource.com/nexus/content/groups/ea</url>
    </pluginRepository>
    <pluginRepository>
      <releases>
        <enabled>false</enabled>
      </releases>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
      <id>snapshot.fusesource.org</id>
      <name>FuseSource Snapshot Repository</name>
      <url>http://repo.fusesource.com/nexus/content/repositories/snapshots</url>
    </pluginRepository>
  </pluginRepositories>
  <build>
    <defaultGoal>install</defaultGoal>
    <plugins>
      <plugin>
        <groupId>org.apache.felix</groupId>
        <artifactId>maven-bundle-plugin</artifactId>
        <version>2.3.7</version>
        <extensions>true</extensions>
        <configuration>
          <instructions>
            <Bundle-SymbolicName>${project.artifactId}</Bundle-SymbolicName>
            <Private-Package>com.mycompany.*</Private-Package>
            <Import-Package>*</Import-Package>
          </instructions>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.camel</groupId>
        <artifactId>camel-maven-plugin</artifactId>
        <version>${camel-version}</version>
        <configuration>
          <useBlueprint>true</useBlueprint>
        </configuration>
       </plugin>
         <!-- fabric8 plugin for using deploying via mvn fabric:deploy -->
       <plugin>
        <groupId>io.fabric8</groupId>
        <artifactId>fabric8-maven-plugin</artifactId>
        <version>${fabic8-version}</version>
      </plugin>

    </plugins>
  </build>

</project>

或者，如果您想计算特定阈值，您可以显示预期结果吗？

PostgreSQL计算阈值查询

3 个答案: