@SelectKey

package com.flying.entity;

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String major;
    private Double score;

    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 Integer getAge() { return age; }
    public void setAge(Integer age) { this.age = age; }
    public String getMajor() { return major; }
    public void setMajor(String major) { this.major = major; }
    public Double getScore() { return score; }
    public void setScore(Double score) { this.score = score; }
}

package com.flying.mapper;

import com.flying.entity.Student;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.SelectKey;

public interface StudentMapper {

    /**
     * 模拟 Oracle 序列场景：插入前先获取序列值作为主键
     * before = true，先执行 SELECT 获取 id，再执行 INSERT
     */
    @SelectKey(statement = "SELECT current_value + 1 FROM id_sequence WHERE seq_name = 'student_seq'",
               keyProperty = "id", keyColumn = "id", before = true, resultType = Integer.class)
    @Insert("INSERT INTO student(id, name, age, major, score) VALUES(#{id}, #{name}, #{age}, #{major}, #{score})")
    int insertWithSequence(Student student);

    /**
     * MySQL 场景：插入后获取 LAST_INSERT_ID
     * before = false，先执行 INSERT，再执行 SELECT LAST_INSERT_ID()
     * 注意：此示例中 student 表 id 为 AUTO_INCREMENT 时才有效，此处仅为演示语法
     */
    @SelectKey(statement = "SELECT LAST_INSERT_ID()",
               keyProperty = "id", keyColumn = "id", before = false, resultType = Integer.class)
    @Insert("INSERT INTO student(name, age, major, score) VALUES(#{name}, #{age}, #{major}, #{score})")
    int insertWithLastInsertId(Student student);
}

package com.flying.test;

import com.flying.entity.Student;
import com.flying.mapper.StudentMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;

public class SelectKeyTest {
    public static void main(String[] args) throws Exception {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
        SqlSession session = factory.openSession();

        StudentMapper mapper = session.getMapper(StudentMapper.class);

        // 1. 模拟 Oracle 序列：插入前获取主键
        System.out.println("=== 插入前获取主键（模拟 Oracle 序列）===");
        Student stu1 = new Student();
        stu1.setName("赵新");
        stu1.setAge(23);
        stu1.setMajor("人工智能");
        stu1.setScore(91.0);

        int rows1 = mapper.insertWithSequence(stu1);
        System.out.println("影响行数: " + rows1);
        System.out.println("回填主键 id: " + stu1.getId());

        // 2. MySQL LAST_INSERT_ID：插入后获取主键
        System.out.println("\n=== 插入后获取主键（MySQL LAST_INSERT_ID）===");
        Student stu2 = new Student();
        stu2.setName("钱多多");
        stu2.setAge(20);
        stu2.setMajor("网络工程");
        stu2.setScore(85.0);

        int rows2 = mapper.insertWithLastInsertId(stu2);
        System.out.println("影响行数: " + rows2);
        System.out.println("回填主键 id: " + stu2.getId());

        session.commit();
        session.close();
    }
}