1、SQL

create table user (
id int primary key,
name varchar(400)
);
insert user info VALUES(1, 'ConstXiong1');


create table info (
user_id int primary key,
name varchar(400)
);
insert into info VALUES(1, '大熊');

create table article (
user_id int,
title varchar(400)
);
insert into article VALUES(1, '文章1');
insert into article VALUES(1, '文章2');

2、Maven 依赖

<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>

    <parent>
        <groupId>constxiong</groupId>
        <artifactId>demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <artifactId>mybatis</artifactId>

    <dependencies>
        <!-- MySQL 8.0.21 驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.21</version>
        </dependency>

        <!-- MyBatis -->
        <dependency>
		  <groupId>org.mybatis</groupId>
		  <artifactId>mybatis</artifactId>
		  <version>3.5.5</version>
		</dependency>

    </dependencies>

    <build>

    </build>
</project>

3、mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://172.31.32.184:3306/constxiong?serverTimezone=UTC&amp;useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="constxiong@123"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="constxiong/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

4、Mapper xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="constxiong.mapper.UserMapper">
    
    <select id="selectUserWithInfo" resultMap="UserWithInfo">
        select user.id, user.name, info.user_id, info.name as info_name from user,info where user.id = info.user_id
    </select>

    <select id="selectUserWithArticles" resultMap="UserWithArticles">
        select user.id, user.name, article.user_id, article.title from user,article where user.id = article.user_id
    </select>

    <resultMap id="UserWithInfo" type="constxiong.po.User">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <association property="info" javaType="constxiong.po.Info">
            <id property="userId" column="user_id"/>
            <result property="name" column="info_name"/>
        </association>
    </resultMap>

    <resultMap id="UserWithArticles" type="constxiong.po.User">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <collection property="articles" ofType="constxiong.po.Article">
            <id property="userId" column="user_id"/>
            <result property="title" column="title"/>
        </collection>
    </resultMap>

</mapper>

5、Mapper 接口

package constxiong.mapper;

import constxiong.po.User;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.List;
import java.util.Map;

/**
 * UserMapper 接口，映射对数据库的操作
 */
public interface UserMapper {

    User selectUserWithInfo();

    User selectUserWithArticles();

}

6、PO 类

package constxiong.po;

import java.util.List;

/**
 * 用户表模型
 */
public class User {
    private Integer id;

    private String name;

    private String mc;

    private Info info;

    private List<Article> articles;

    public User() {
    }

    public User(Integer id, String name) {
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMc() {
        return mc;
    }

    public void setMc(String mc) {
        this.mc = mc;
    }

    public Info getInfo() {
        return info;
    }

    public void setInfo(Info info) {
        this.info = info;
    }

    public List<Article> getArticles() {
        return articles;
    }

    public void setArticles(List<Article> articles) {
        this.articles = articles;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", mc='" + mc + '\'' +
                ", info=" + info +
                ", articles=" + articles +
                '}';
    }
}

package constxiong.po;

public class Info {

    private int userId;

    private String name;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Info{" +
                "userId=" + userId +
                ", name=" + name +
                '}';
    }
}

package constxiong.po;

public class Article {

    private int userId;

    private String title;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @Override
    public String toString() {
        return "Article{" +
                "userId=" + userId +
                ", title='" + title + '\'' +
                '}';
    }
}

7、测试代码