用Java评估SQL表达式？ [英] Evaluate SQL expressions in Java?

问题描述

在我们的项目中，我们需要在没有任何数据库服务器的情况下评估SQL语句。你能建议任何能够评估基于数学的SQL语句并返回结果的免费Java库吗？

In our project, we need to evaluate SQL statements without any database server. Can you suggest any free Java library that has the ability to evaluate math based SQL statements and return the result?

例如;

SELECT 2 * 2 AS RESULT

4

可能会被称为 int result = SQLEvaluator.evaluate（SELECT 2 * 2 AS RESULT）;

推荐答案

使用 ZQL 可以实现这一点，如下面的代码所示。但我认真建议你选择一个简单的嵌入式数据库，如 H2 （此处示例）并使用相反（项目健康状况要高得多）。

It is possible to achieve that using ZQL as seen in the code below. But I seriously advise you pick a simple embedded database such as H2 (example here) and use it instead (the project health is much higher).

public class H2ExpEval {
    public static void main(String... args) throws Exception {
        evaluateUsingH2("SELECT 2+2");
        evaluateUsingH2("SELECT 3+7-5");
        evaluateUsingH2("SELECT 2*2*2+1");
    }

    private static void evaluateUsingH2(String sql) throws Exception {
        Class.forName("org.h2.Driver");
        // opens an in-memory database: no files are saved and it's all quicker
        Connection conn = DriverManager.getConnection("jdbc:h2:mem:");
        Statement stat = conn.createStatement();
        ResultSet rs = stat.executeQuery(sql);
        if (rs.next()) {
            System.out.println(rs.getString(1));
        }
        stat.close(); conn.close();
    }
}

输出：

4
5
9

要使用它，请将其添加到 pom.xml ：

To use it, add this to your pom.xml:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.3.171</version>
</dependency>

使用ZQL：

Using ZQL:

public class ZqlEvalDemo {
    public static void main(String args[]) throws Exception {
        System.out.println(evaluate("SELECT 2+2 FROM RESULT;"));
        System.out.println(evaluate("SELECT 3+7-5 FROM RESULT;"));
        System.out.println(evaluate("SELECT 2*2*2+1 FROM RESULT;"));
    }

    private static ZqlParser p = new ZqlParser();
    private static Object evaluate(String s) throws Exception {
        p.initParser(new java.io.ByteArrayInputStream(s.getBytes()));
        ZStatement st = p.readStatement();
        ZSelectItem zSelectItem = ((ZQuery) st).getSelect().get(0);
        ZExpression exp = (ZExpression) zSelectItem.getExpression();
        return new ZEval().evalExpValue(new ZTuple(), exp);
    }
}

输出：

4.0
5.0
9.0

对于依赖项，可以从 ZQL页面下载，或者为了测试目的，将其添加到你的 pom.xml （测试目的，因为我们不知道是谁维护了那个存储库）：

For the dependencies, either download from the ZQL Page or, for testing purposes, add this to your pom.xml (testing purposes because we don't know who maintains that repository):

<dependencies>
  <dependency>
    <groupId>com.experlog</groupId>
    <artifactId>zql</artifactId>
    <version>1.0</version>
  </dependency>
</dependencies>
<repositories>
  <repository>
    <id>zql</id>
    <name>zql</name>
    <url>http://dbappserv.cis.upenn.edu:8080/artifactory/ext-releases-local</url>
  </repository>
</repositories>

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