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MyBatis 多表关联查询
环境信息：
OS：Mac OS
Jdk：JavaSE 8
Ide：Idea Ultimate
MySQL：8.0.16
MyBatis：3.5.2
Spring Boot：2.1.7.RELEASE
1.数据库表信息
1.1 数据库表关系图
学生表：t_student
成绩表：t_score
关系图：
1.2 实体类
Student对应t_student表
@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class Student {
private Integer id;
private String name;
private Integer age;
private String sex;
private String hobbies;
private String address;
}
Score对应t_score表
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class Score {
private Integer id;
//学生编号
private Integer studentId;
private String studentName;
//科目
private String subject;
//科目成绩
private Integer subjectScore;
}
注：@Data，@Builder，@AllArgsConstructor，@NoArgsConstructor为lombok的注解
1.3 表数据
t_student：
t_score：
2.多表关联查询种类
Student与Score是一对多的关系，他们连个关联查询有两种情况：
- 2.1 一个学生的所有成绩
StudentScores
@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class StudentScores {
private Integer id;
private String name;
private Integer age;
private String sex;
private List<Score> scoreList; //t_score查询出的数据映射成一个List<Score>
}
- 2.2 一个学生的某一门成绩
StudentScore
@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class StudentScore {
private Integer id;
private String name;
private Integer age;
private String sex;
private Score score; //t_score查询出的数据映射成一个Score
}
3.MyBatis多表关联查询实现
在标签中使用和标签实现#2中的两种情况：
- association - 一种复杂的结果; 许多结果将汇总到这个类型中, 可关联是resultMap自身，或者可以引用一个
- collection - 复杂类型的集合, 可关联是resultMap自身，或者可以引用一个
意思就是：映射成的字段为一个复杂对象时用association，映射成的字段为一个集合,时用collection，而且他们都可以引用已经存在的resultMap;
详见 http://www.mybatis.org/mybatis-3/sqlmap-xml.html#Result_Maps
3.1 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="com.wxx.sbmm.mapper.StudentMapper">
<!--映射成 List<Score> scoreList-->
<resultMap id="studentScoreListResultMap" type="com.wxx.sbmm.domain.StudentScores">
<id column="aid" jdbcType="INTEGER" property="id"/>
<result column="name" jdbcType="VARCHAR" javaType="String" property="name"/>
<result column="age" javaType="Integer" property="age"/>
<result column="sex" javaType="String" property="sex"/>
<collection property="scoreList" javaType="List" ofType="Score">
<id column="bid" jdbcType="INTEGER" property="id"/>
<result property="studentId" column="student_id"/>
<result property="studentName" column="student_name"/>
<result property="subject" column="subject"/>
<result property="subjectScore" column="subject_score"/>
</collection>
</resultMap>
<!--映射成 Score score-->
<resultMap id="studentScoreResultMap" type="com.wxx.sbmm.domain.StudentScore">
<id column="aid" jdbcType="BIGINT" javaType="Integer" property="id"/>
<result property="name" jdbcType="VARCHAR" javaType="String" column="name"/>
<result property="age" column="age" jdbcType="VARCHAR" javaType="Integer"/>
<result property="sex" column="sex" jdbcType="VARCHAR" javaType="String"/>
<association property="score" javaType="com.wxx.sbmm.domain.Score">
<id property="id" column="bid"/>
<result property="studentId" column="student_id"/>
<result property="studentName" column="student_name"/>
<result property="subject" column="subject"/>
<result property="subjectScore" column="subject_score"/>
</association>
</resultMap>
<!-- 联合查询 1 findStudentScoreList -->
<select id="findStudentScoreList" parameterType="Integer" resultMap="studentScoreListResultMap">
select
a.id aid,
a.name name,
a.age age,
a.sex sex,
b.id bid,
b.student_id student_id,
b.student_name student_name,
b.subject subject,
b.subject_score subject_score
from t_student a
left join t_score b
on a.id=b.student_id
</select>
<!-- 联合查询 2 findStudentScore-->
<select id="findStudentScore" resultMap="studentScoreResultMap">
select
a.id aid,
a.name name,
a.age age,
a.sex sex,
b.id bid,
b.student_id student_id,
b.student_name student_name,
b.subject subject,
b.subject_score subject_score
from t_student a
left join t_score b
on a.id=b.student_id
where b.subject = 'English'
and a.name = b.student_name
</select>
</mapper>
3.2 查询结果
-
1.studentScoreList
-
2.studentScoreList
4.附录：数据库初始化信息
数据库为：studentService
建数据库语句：CREATE SCHEMA `studentService` DEFAULT CHARACTER SET utf8 ;
包含两个表，针对它们进行关联查询：
学生表：t_student
成绩表：t_score
4.1 建表语句
初始化库表SQL：
CREATE DATABASE IF NOT EXISTS `studentService`;
CREATE TABLE IF NOT EXISTS `t_student` (
`id` INT NOT NULL AUTO_INCREMENT COMMENT 'ID',
`name` VARCHAR(255) DEFAULT "" COMMENT '姓名',
`age` INT DEFAULT 10 COMMENT '年龄',
`sex` VARCHAR(255)DEFAULT "Male" COMMENT '性别',
`hobbies` VARCHAR(255) DEFAULT "" COMMENT '爱好',
`address` VARCHAR(255) DEFAULT "" COMMENT '住址',
PRIMARY KEY(`id`),
UNIQUE INDEX `idx_student_name_address` (`name`,`address`) USING BTREE
)ENGINE = INNODB DEFAULT CHARSET=utf8 AUTO_INCREMENT = 1 COMMENT '学生表';
CREATE TABLE IF NOT EXISTS `t_score` (
`id` INT NOT NULL AUTO_INCREMENT COMMENT 'ID',
`student_id` INT DEFAULT 0 COMMENT '学生ID',
`student_name` VARCHAR(255) DEFAULT "" COMMENT '学生姓名',
`subject` VARCHAR(255) DEFAULT "" COMMENT '学科',
`subject_score` INT COMMENT '学科成绩',
PRIMARY KEY(`id`),
UNIQUE INDEX `idx_score_studentname_subject` (`student_name`,`subject`) USING BTREE ,
FOREIGN KEY (student_id) REFERENCES t_student (id)
)ENGINE = INNODB DEFAULT CHARSET=utf8 AUTO_INCREMENT = 1 COMMENT '学生成绩表';
4.2 插入数据
初始化数据SQL：
INSERT INTO t_student (name,age, sex, hobbies, address)
SELECT "Even",9,"Male","ShuXue,English","XiAn" FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_student WHERE name = "Even");
INSERT INTO t_student (name,age, sex, hobbies, address)
SELECT "Weison",11,"Male","XuWen,WuLi","HeNan" FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_student WHERE name = "Weison");
INSERT INTO t_student (name,age, sex, hobbies, address)
SELECT "Angule",13,"Female","XuWen,English","Chengdu" FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_student WHERE name = "Angule");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 1,"Even","YuWen",90 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Even" and subject ="YuWen");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 1,"Even","ShuXue",89 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Even" and subject ="ShuXue");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 1,"Even","English",67 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Even" and subject ="English");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 2,"Weison","YuWen",69 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Weison" and subject ="YuWen");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 2,"Weison","ShuXue",94 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Weison" and subject ="ShuXue");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 2,"Weison","English",82 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Weison" and subject ="English");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 3,"Angule","YuWen",58 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Angule" and subject ="YuWen");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 3,"Angule","ShuXue",73 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Angule" and subject ="ShuXue");
INSERT INTO t_score (student_id,student_name, subject, subject_score)
SELECT 3,"Angule","English",91 FROM DUAL WHERE NOT EXISTS(SELECT 1 FROM t_score WHERE student_name = "Angule" and subject ="English");
commit;
代码 --> https://github.com/WeisonWei/springboot-aggregation/tree/master/springboot-mvc-mybatis