Question

我试图在我的战争中访问一个SQLLite数据库，其中一些列的名称中有空格。

我在SO上看到了上一个问题Read data from SQLite where column name contains spaces，但解决方案不起作用：

我知道我应该用``，“”或[]来逃避列名称，但这对我来说都不起作用，我得到以下每个转义字符的异常，空格或没有空格在列名称中：

java.sql.SQLException: no such column: '[class of worker]'
java.sql.SQLException: no such column: '"age"'

与`相同，并且在SO上没有很好地逃脱

同时，该请求适用于没有空格的未转义列名称（例如“年龄”或“教育”）

我的代码中的请求看起来很好：

SELECT DISTINCT `class of worker`, COUNT(*) as countt, ROUND(CAST(SUM(age) AS FLOAT)/COUNT(*),3) as avgage FROM census_learn_sql GROUP BY `class of worker` ORDER BY countt DESC

这是访问db的代码：

public Results getColumnValues(String column){

    column = "`" + column + "`"; //handle space in column names
    String sql = "SELECT DISTINCT "+column+", COUNT(*) as countt, ROUND(CAST(SUM(age) AS FLOAT)/COUNT(*),3) as avgage FROM census_learn_sql GROUP BY "
                    +column+" ORDER BY countt DESC";

    Results results = new Results();
    int count = 0;
    int clippedOutRows = 0;

    try (Connection conn = this.connect();
         Statement stmt  = conn.createStatement();
         ResultSet rs    = stmt.executeQuery(sql)){

        while (rs.next()) {
            if (count >= 100){
                clippedOutRows += rs.getInt("countt");
            }
            else {
                results.getResults().add(new RowResult(rs.getString(column),
                        rs.getInt("countt"),
                        rs.getDouble("avgage")));
            }

            count++;
        }

        results.setClippedOutRows(clippedOutRows);
        results.setClippedOutValues(count > 99 ? count - 99 : 0);
    } catch (SQLException e) {
        System.out.println(e.getMessage());
    }

    return results;
}

这是我的pom文件依赖项：

<properties>
        <!-- maven-compiler-plugin -->
        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
        <version.javaee>7.0</version.javaee>
        <version.resteasy>3.0.10.Final</version.resteasy>
        <version.jackson>2.4.1</version.jackson>
        <version.junit>4.11</version.junit>
        <version.assertj>1.6.1</version.assertj>
        <version.commons>3.2.1</version.commons>
    </properties>


    <dependencies>
        <dependency>
            <groupId>org.jboss.resteasy</groupId>
            <artifactId>resteasy-jaxrs</artifactId>
            <version>${version.resteasy}</version>
        </dependency>
        <dependency>
            <groupId>org.jboss.resteasy</groupId>
            <artifactId>resteasy-servlet-initializer</artifactId>
            <version>${version.resteasy}</version>
        </dependency>
        <dependency>
            <groupId>org.jboss.resteasy</groupId>
            <artifactId>resteasy-jackson-provider</artifactId>
            <version>${version.resteasy}</version>
        </dependency>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>${version.javaee}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>commons-collections</groupId>
            <artifactId>commons-collections</artifactId>
            <version>${version.commons}</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${version.junit}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.assertj</groupId>
            <artifactId>assertj-core</artifactId>
            <version>${version.assertj}</version>
            <scope>test</scope>
        </dependency>
        <!-- SQLite JDBC library -->
        <dependency>
           <groupId>org.xerial</groupId>
           <artifactId>sqlite-jdbc</artifactId>
           <version>3.8.11.2</version>
        </dependency>
    </dependencies>

我不知道我在这里做错了什么，这是一个依赖性问题吗？

提前感谢您的帮助

Answer 1

您正在修改字符串值column以分隔列名

column = "`" + column + "`"; //handle space in column names
String sql = "SELECT DISTINCT "+column+", COUNT(*) ...

但是当您从ResultSet中检索值时，您使用的是分隔列名称

rs.getString(column)

相当于

rs.getString("`class of worker`")

并且ResultSet不包含该名称的列：名称只是class of worker。换句话说，SQL命令需要分隔符，但ResultSet#getString方法不需要。

因此，不应修改column变量，而应该在sql字符串中放置反引号（或双引号或方括号; SQLite支持所有这些）

// column = "`" + column + "`"; // do not handle space in column names here, do it below
String sql = "SELECT DISTINCT `" + column + "`, COUNT(*) ...

然后你的rs.getString(column)应该可以正常工作。

SQLite列，名称中包含空格

1 个答案: