前置准备

因为连接PostgreSQL需要先安装PG，所以以下给出PG的简单安装教程：
window安装PostgreSQL

对应的建表语句：

DROP TABLE IF EXISTS student;
CREATE TABLE student (
  id serial NOT NULL,
  name varchar(100) NOT NULL,
  sex varchar(5) NOT NULL,
  PRIMARY KEY (id)
);

INSERT INTO student (id, name, sex) VALUES (1, '小明', '男');
INSERT INTO student (id, name, sex) VALUES (2, '小红', '女');

CREATE TABLE IF NOT EXISTS score
(
    id integer NOT NULL,
    student_id integer NOT NULL,
    grade integer NOT NULL,
    PRIMARY KEY (id)
);

insert into score(id,student_id,grade)values(1,1,80);
insert into score(id,student_id,grade)values(2,2,90);

关于PG如何建表：
PostgreSQL表的创建

代码

下面是连接JDBC并进行查询的代码，注意几个参数：

org.postgresql.Driver，该参数需要jar包，通过maven配置更加简单。
jdbc:postgresql://localhost:5432/School，连接的本地postgreSQL，School是数据库名称
user和passwd自然不用说，配置PG的时候自然会设置，默认user为postgres

import java.sql.*;

public class PostgreSQLJDBC {
    public static void main( String args[] ) {
        Connection conn = null;
        Statement stmt = null;
        try {
            // 加载 PostgreSQL 驱动类
            Class.forName("org.postgresql.Driver");

            // 创建数据库连接
            String url = "jdbc:postgresql://localhost:5432/School";
            String user = "postgres";
            String password = "123456";
            conn = DriverManager.getConnection(url, user, password);

            // 创建 Statement 对象
            stmt = conn.createStatement();

            // 执行查询语句
            String sql = "SELECT * FROM student";
            ResultSet rs = stmt.executeQuery(sql);

            // 处理查询结果
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String sex = rs.getString("sex");
                System.out.println(id + "\t" + name + "\t" + sex);
            }

            // 关闭 ResultSet、Statement 和 Connection 对象
            rs.close();
            stmt.close();
            conn.close();

        } catch(SQLException se) {
            // 处理 JDBC 异常
            se.printStackTrace();
        } catch(Exception e) {
            // 处理 Class.forName 异常
            e.printStackTrace();
        } finally {
            // 关闭资源
            try {
                if(stmt!=null) stmt.close();
            } catch(SQLException se2) {
            }
            try {
                if(conn!=null) conn.close();
            } catch(SQLException se3) {
                se3.printStackTrace();
            }
        }
    }
}

pom.xml配置文件：

<?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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>mvn_calcite_test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.calcite</groupId>
            <artifactId>calcite-core</artifactId>
            <version>1.19.0</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-nop</artifactId>
            <version>1.7.2</version>
            <type>jar</type>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.2.18</version>
        </dependency>
    </dependencies>



</project>