我有一个表，其中的条目如下：
表中的第一个条目是时间戳4，依此类推。
Id state timestamp f disabled_reason 9 e enabled 8 d disabled_reason2 7 c disabled_reason3 6 b disabled_reason4 5 a enabled 4
我想创建一个具有以下逻辑的列： 如果允许状态，请清除agg_state，否则创建一对状态时间戳，并将其添加到agg_state列对中（如果存在）。
因此输出表将如下所示：
Id state timestamp agg_state
f disabled_reason 9 (disabled_reason,9)
e enabled 8
d disabled_reason2 7 (disabled_reason4,5)
(disabled_reason3,6)
(disabled_reason2,7)
c disabled_reason3 6 (disabled_reason4,5)
(disabled_reason3,6)
b disabled_reason4 5 (disabled_reason4,5)
a enabled 4
有人知道是否可以在SQL中执行此逻辑？
答案 0 :(得分：0)
您可以在任何SQL-92兼容数据库中使用case语句。 您还可以在SQL Server 2012及更高版本中使用iif：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<groupId>work.basil.example</groupId>
<artifactId>acme</artifactId>
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<packaging>war</packaging>
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<repository>
<id>Vaadin Directory</id>
<url>https://maven.vaadin.com/vaadin-addons</url>
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<version>${vaadin.version}</version>
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<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
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<artifactId>vaadin</artifactId>
<exclusions>
<!-- Webjars are only needed when running in Vaadin 13 compatibility mode -->
<exclusion>
<groupId>com.vaadin.webjar</groupId>
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<artifactId>slf4j-simple</artifactId>
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<dependency>
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<dependency>
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<artifactId>vaadin-testbench</artifactId>
<scope>test</scope>
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<groupId>org.apache.maven.plugins</groupId>
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<version>3.8.1</version>
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<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-maven-plugin</artifactId>
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<configuration>
<!-- If using IntelliJ IDEA with autocompilation, this
might cause lots of unnecessary compilations in the
background.-->
<scanIntervalSeconds>2</scanIntervalSeconds>
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Take care of synchronizing java dependencies and imports in
package.json and main.js files.
It also creates webpack.config.js if not exists yet.
-->
<plugin>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-maven-plugin</artifactId>
<version>${vaadin.version}</version>
<executions>
<execution>
<goals>
<goal>prepare-frontend</goal>
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<plugin>
<groupId>com.github.eirslett</groupId>
<artifactId>frontend-maven-plugin</artifactId>
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https://repo1.maven.org/maven2/com/github/eirslett/frontend-maven-plugin/ -->
<version>1.8.0</version>
<executions>
<execution>
<!-- optional: you don't really need execution ids, but it looks nice in your build log. -->
<id>install node and npm</id>
<goals>
<goal>install-node-and-npm</goal>
</goals>
<!-- optional: default phase is "generate-resources" -->
<phase>generate-resources</phase>
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<!-- optional: with node version greater than 4.0.0 will use npm provided by node distribution -->
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<id>production</id>
<properties>
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</properties>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
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<groupId>com.vaadin</groupId>
<artifactId>vaadin-maven-plugin</artifactId>
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<profile>
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<plugin>
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<stopPort>8081</stopPort>
<stopWait>5</stopWait>
<stopKey>${project.artifactId}</stopKey>
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<execution>
<id>start-jetty</id>
<phase>pre-integration-test</phase>
<goals>
<goal>deploy-war</goal>
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<execution>
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<webdriver.chrome.driver>${webdriver.chrome.driver}</webdriver.chrome.driver>
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<artifactId>driver-binary-downloader-maven-plugin</artifactId>
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<configuration>
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</onlyGetDriversForHostOperatingSystem>
<rootStandaloneServerDirectory>
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<downloadedZipFileDirectory>
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<goals>
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