一、MyBatis环境搭建
1.1、数据的准备
CREATE DATABASE IF NOT EXISTS db_test;
USE db_test;
CREATE TABLE IF NOT EXISTS t_emp(
emp_id int PRIMARY KEY auto_increment,
emp_name VARCHAR(30),
age INT,
sex CHAR,
dept_id INT
);
CREATE TABLE IF NOT EXISTS t_dept(
dept_id INT PRIMARY KEY auto_increment,
dept_name VARCHAR(30)
);
INSERT INTO t_dept(dept_name)
VALUES('魔法部'),
('超能力部'),
('灵异部');
INSERT INTO t_emp(emp_name,age,sex,dept_id)
VALUES('Sakura',10,'女',1),
('Mikoto',14,'女',2),
('Shana',15,'女',1),
('Kikyō',18,'女',3),
('Kagome',15,'女',3);
1.2、导入jar包
通过 maven 的方式导入 jar包，打包方式设置为 jar 包即可。
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.7</version>
</dependency>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.29</version>
</dependency>
<!-- junit 测试程序 -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
1.3、创建核心配置文件
创建 MyBatis 的核心配置文件，习惯上命名为 mybatis-config.xml，这个文件名仅仅只是建议，并非强制要求。配置 MyBatis 的核心配置文件中的标签必须按照固定的顺序：
properties --> settings --> typeAliases --> typeHandlers --> objectFactory --> objectWrapperFactory --> reflectorFactory --> plugins --> environments --> databaseIdProvider --> mappers
<?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>
<!-- 引入数据库连接信息的配置文件 -->
<properties resource="jdbc.properties"/>
<!-- 设置类型别名 -->
<typeAliases>
<!-- 以包为单位，将包下所有的类型设置默认的类型别名，即类名且不区分大小写 -->
<package name="star.light.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<!-- 设置连接数据库的驱动 -->
<property name="driver" value="${jdbc.driver}"/>
<!-- 设置连接数据库的地址 -->
<property name="url" value="${jdbc.url}"/>
<!-- 设置连接数据库的用户名 -->
<property name="username" value="${jdbc.username}"/>
<!-- 设置连接数据库的密码 -->
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!--引入映射文件-->
<mappers>
<!--
以包为单位引入映射文件，要求：
1、mapper接口所在的包与映射文件所在的包一致
2、mapper接口要和映射文件一致
-->
<package name="star.light.mapper"/>
</mappers>
</configuration>
数据库连接信息的配置文件：jdbc.properties
jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/db_test
jdbc.username=root
jdbc.password=abc123
1.4、创建实体类
package star.light.pojo;
public class Employee {
private Integer empId;
private String empName;
private Integer age;
private String sex;
private Department department;
public Employee() {
}
public Employee(Integer empId, String empName, Integer age, String sex) {
this.empId = empId;
this.empName = empName;
this.age = age;
this.sex = sex;
}
public Employee(Integer empId, String empName, Integer age, String sex, Department department) {
this.empId = empId;
this.empName = empName;
this.age = age;
this.sex = sex;
this.department = department;
}
public Integer getEmpId() {
return empId;
}
public void setEmpId(Integer empId) {
this.empId = empId;
}
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Department getDepartment() {
return department;
}
public void setDepartment(Department department) {
this.department = department;
}
@Override
public String toString() {
return "Employee{" +
"empId=" + empId +
", empName='" + empName + '\'' +
", age=" + age +
", sex='" + sex + '\'' +
", department=" + department +
'}';
}
}
package star.light.pojo;
import java.util.List;
public class Department {
private Integer deptId;
private String deptName;
private List<Employee> employees;
public Department() {
}
public Department(Integer deptId, String deptName) {
this.deptId = deptId;
this.deptName = deptName;
}
public Department(Integer deptId, String deptName, List<Employee> employees) {
this.deptId = deptId;
this.deptName = deptName;
this.employees = employees;
}
public Integer getDeptId() {
return deptId;
}
public void setDeptId(Integer deptId) {
this.deptId = deptId;
}
public String getDeptName() {
return deptName;
}
public void setDeptName(String deptName) {
this.deptName = deptName;
}
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
@Override
public String toString() {
return "Department{" +
"deptId=" + deptId +
", deptName='" + deptName + '\'' +
", employees=" + employees +
'}';
}
}
1.5、创建mapper接口
MyBatis 中的 mapper 接口相当于以前的 dao。但是区别在于，mapper 仅仅是接口，我们不需要提供实现类。
package star.light.mapper;
public interface EmpMapper {
/**
* MyBatis 面向接口编程的两个一致：
* 1、映射文件的 namespace 要和 mapper 接口的全类名保持一致
* 2、映射文件中 SQL 语句的 id 要和 mapper 接口中方法名一致
*/
}
package star.light.mapper;
public interface DeptMapper{
/**
* MyBatis 面向接口编程的两个一致：
* 1、映射文件的 namespace 要和 mapper 接口的全类名保持一致
* 2、映射文件中 SQL 语句的 id 要和 mapper 接口中方法名一致
*/
}
1.6、创建MyBatis的映射文件
映射文件的命名应该为 表所对应的实体类的类名+Mapper.xml。一个映射文件对应一个实体类，对应一张表的操作。MyBatis映射文件用于编写SQL，访问以及操作表中的数据。
<?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="star.light.mapper.EmpMapper">
</mapper>
<?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="star.light.mapper.DeptMapper">
</mapper>
1.7、封装SqlSessionUtil工具类
package star.light.util;
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.IOException;
import java.io.InputStream;
public class SqlSessionUtil {
public static SqlSession getSqlSession(){
SqlSession sqlSession = null;
try {
InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
sqlSession = sqlSessionFactory.openSession(true);
} catch (IOException e) {
e.printStackTrace();
}
return sqlSession;
}
}
二、字段名与属性名不一致问题
2.1、查询的字段设置别名
测试程序：
package star.light.test;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import star.light.mapper.EmpMapper;
import star.light.pojo.Employee;
import star.light.util.SqlSessionUtil;
public class ResultMapTest {
@Test
public void testGetEmployeeByEmpId(){
SqlSession sqlSession = SqlSessionUtil.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Employee employee = mapper.getEmployeeByEmpId(1);
System.out.println(employee);
}
}
重写 EmpMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Employee;
public interface EmpMapper {
Employee getEmployeeByEmpId(@Param("empId") Integer empid); // 根据id查询员工的信息
}
重写 EmpMapper.xml 配置文件：
<?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="star.light.mapper.EmpMapper">
<!-- Employee getEmployeeByEmpId(@Param("empId") Integer empid); -->
<select id="getEmployeeByEmpId" resultType="Employee">
<!--
字段名和属性名不一致的情况，如何处理映射关系：
为查询的字段设置别名，和属性名保持一致
-->
select emp_id empId,emp_name empName,age,sex from t_emp where emp_id = #{empId}
</select>
</mapper>
2.2、核心配置文件中设置全局配置
在 mybatis-config.xml 配置文件中 <configuration> 中的 <properties> 后添加如下信息：
<settings>
<!-- 将下划线映射为驼峰 -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
重写 EmpMapper.xml 配置文件：
<?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="star.light.mapper.EmpMapper">
<!-- Employee getEmployeeByEmpId(@Param("empId") Integer empid); -->
<select id="getEmployeeByEmpId" resultType="Employee">
<!--
字段名和属性名不一致的情况，如何处理映射关系：
当字段符合MySQL的要求使用_命令法，而属性名符合Java的要求使用驼峰命名法
此时可以在 MyBatis的核心配置文件中设置一个全局配置，可以自动将下划线映射为驼峰
-->
select emp_id,emp_name,age,sex from t_emp where emp_id = #{empId}
</select>
</mapper>
其中，ReusltMapTest 测试程序，EmpMapper 接口内容同上；
2.3、自定义映射处理
重写 EmpMapper.xml 配置文件：
<?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="star.light.mapper.EmpMapper">
<!--
resultMap：设置自定义映射
属性：
id：表示自定义映射的唯一标识
type：查询的数据要映射的实体类的类型
子标签：
id：设置主键的映射关系
result：设置普通字段的映射关系
association：设置多对一的映射关系
collection：设置一对多的映射关系
属性：
property：设置映射关系中实体类中的属性名
column：设置映射关系中表中的字段名
-->
<resultMap id="empAndDeptResultMap" type="Emp">
<id column="emp_id" property="empId"></id>
<result column="emp_name" property="empName"></result>
<result column="age" property="age"></result>
<result column="sex" property="sex"></result>
</resultMap>
<!-- Employee getEmployeeByEmpId(@Param("empId") Integer empid); -->
<select id="getEmployeeByEmpId" resultMap="empResultMap">
select emp_id,emp_name,age,sex from t_emp where emp_id = #{empId}
</select>
</mapper>
其中，ReusltMapTest 测试程序，EmpMapper 接口内容同上；
三、多对一映射关系
3.1、级联方式处理映射关系
测试程序：
package star.light.test;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import star.light.mapper.EmpMapper;
import star.light.pojo.Employee;
import star.light.util.SqlSessionUtil;
public class ResultMapTest {
@Test
public void testGetEmpAndDeptByEmpId(){
SqlSession sqlSession = SqlSessionUtil.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Employee employee = mapper.getEmpAndDeptByEmpId(1);
System.out.println(employee);
}
}
EmpMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Employee;
public interface EmpMapper {
Employee getEmpAndDeptByEmpId(@Param("empId") Integer empid); // 获取员工以及所对应的部门信息
}
EmpMapper.xml 配置文件：
<?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="star.light.mapper.EmpMapper">
<resultMap id="empAndDeptResultMap" type="Employee">
<id column="emp_id" property="empId"></id>
<result column="emp_name" property="empName"></result>
<!-- 使用级联方式处理多对一映射关系 -->
<result column="dept_id" property="department.deptId"></result>
<result column="dept_name" property="department.deptName"></result>
</resultMap>
<!-- Employee getEmpAndDeptByEmpId(@Param("empId") Integer empid); -->
<select id="getEmpAndDeptByEmpId" resultMap="empAndDeptResultMap">
select emp_id,emp_name,age,sex,t_dept.dept_id,dept_name
from t_emp
left join t_dept on t_emp.dept_id = t_dept.dept_id
where emp_id = #{empId}
</select>
</mapper>
3.2、association标签处理映射关系
EmpMapper.xml 配置文件：
<?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="star.light.mapper.EmpMapper">
<resultMap id="empAndDeptResultMap" type="Employee">
<id column="emp_id" property="empId"></id>
<result column="emp_name" property="empName"></result>
<!--
使用association标签处理多对一映射关系（处理实体类类型属性）
property：设置需要处理映射关系的属性的属性名
javaType：设置要处理的出行的类型
-->
<association property="department" javaType="Department">
<id column="dept_id" property="deptId"></id>
<result column="dept_name" property="deptName"></result>
</association>
</resultMap>
<!-- Employee getEmpAndDeptByEmpId(@Param("empId") Integer empid); -->
<select id="getEmpAndDeptByEmpId" resultMap="empAndDeptResultMap">
select emp_id,emp_name,age,sex,t_dept.dept_id,dept_name
from t_emp
left join t_dept on t_emp.dept_id = t_dept.dept_id
where emp_id = #{empId}
</select>
</mapper>
其中，ReusltMapTest 测试程序，EmpMapper 接口内容同上；
3.3、分步查询
测试程序：
package star.light.test;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import star.light.mapper.EmpMapper;
import star.light.pojo.Employee;
import star.light.util.SqlSessionUtil;
public class ResultMapTest {
@Test
public void testGetEmpAndDeptByEmpId(){
SqlSession sqlSession = SqlSessionUtil.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Employee employee = mapper.getEmpAndDeptByStepOne(1);
System.out.println(employee);
}
}
EmpMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Employee;
public interface EmpMapper {
Employee getEmpAndDeptByStepOne(@Param("empId") Integer empId); //通过分步查询员工以及所对应的部门信息的第一步
}
EmpMapper.xml 配置文件
<?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="star.light.mapper.EmpMapper">
<resultMap id="empAndDeptByStepResultMapOne" type="Employee">
<id column="emp_id" property="empId"></id>
<result column="emp_name" property="empName"></result>
<!--
使用association标签处理多对一映射关系（处理实体类类型属性）
property：设置需要处理映射关系的属性的属性名
select：设置分步查询的sql的唯一标识
column：将查询出的某个字段作为分步查询的sql的条件
-->
<association property="department"
select="star.light.mapper.DeptMapper.getEmpAndDeptByStepTwo"
column="dept_id">
</association>
</resultMap>
<!-- Employee getEmpAndDeptByStepOne(@Param("empId") Integer empId); -->
<select id="getEmpAndDeptByStepOne" resultMap="empAndDeptByStepResultMapOne">
select emp_id,emp_name,age,sex,dept_id from t_emp where emp_id = #{empId}
</select>
</mapper>
DeptMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Department;
public interface DeptMapper {
Department getEmpAndDeptByStepTwo(@Param("deptId") Integer deptId); // 通过分步查询查询员工以及所对应的部门信息的第二部
}
DeptMapper.xml 配置文件：
<?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="star.light.mapper.DeptMapper">
<resultMap id="empAndDeptByStepResultMapTwo" type="Department">
<id column="dept_id" property="deptId"></id>
<result column="dept_name" property="deptName"></result>
</resultMap>
<!-- Department getEmpAndDeptByStepTwo(@Param("deptId") Integer deptId); -->
<select id="getEmpAndDeptByStepTwo" resultMap="empAndDeptByStepResultMapTwo">
select dept_id,dept_name from t_dept where dept_id = #{deptId}
</select>
</mapper>
分步查询可以实现延迟加载，但是必须在核心配置文件中设置全局配置信息：
lazyLoadingEnabled：延迟加载的全局开关。当开启时，所有关联对象都会延迟加载
aggressiveLazyLoading：当开启时，任何方法的调用都会加载该对象的所有属性。否则，每个属性会按需加载。此时就可以实现按需加载，获取的数据是什么，就只会执行相应的 sql。
<settings>
<!-- 开启延迟加载 -->
<setting name="lazyLoadingEnabled" value="true"/>
<!-- 按需加载 -->
<setting name="aggressiveLazyLoading" value="false"/>
</settings>
设置全局设置后，对所有的分步查询都有效果，如果某个分步查询不想实现延迟加载，此时可以在相对应的 MyBatis 的映射文件中通过 <association> 和 <collection> 中的 fetchType 属性设置当前的分步查询是否使用延迟加载，** fetchType="lazy (延迟加载)** | eager (立即加载)"。
四、一对多映射关系
4.1、collection标签处理映射关系
测试程序：
package star.light.test;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import star.light.mapper.DeptMapper;
import star.light.pojo.Department;
import star.light.util.SqlSessionUtil;
public class ResultMapTest {
@Test
public void getDeptAndEmpByDeptId(){
SqlSession sqlSession = SqlSessionUtil.getSqlSession();
DeptMapper mapper = sqlSession.getMapper(DeptMapper.class);
Department department = mapper.getDeptAndEmpByDeptId(1);
System.out.println(department);
}
}
DeptMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Department;
public interface DeptMapper {
Department getDeptAndEmpByDeptId(@Param("deptId") Integer deptId); // 查询部门以及部门中的员工信息
}
DeptMapper.xml 配置文件：
<?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="star.light.mapper.DeptMapper">
<resultMap id="deptAndEmpResultMap" type="Department">
<id column="dept_id" property="deptId"></id>
<result column="dept_name" property="deptName"></result>
<!--
collection处理一对多映射关系（处理集合类型的属性）
property：设置需要处理映射关系的属性的属性名
ofType：设置集合类型的属性中存储的数据的类型
-->
<collection property="employees" ofType="Employee">
<id column="emp_id" property="empId"></id>
<result column="emp_name" property="empName"></result>
<result column="age" property="age"></result>
<result column="sex" property="sex"></result>
</collection>
</resultMap>
<!-- Department getDeptAndEmpByDeptId(@Param("deptId") Integer deptId); -->
<select id="getDeptAndEmpByDeptId" resultMap="deptAndEmpResultMap">
SELECT t_dept.dept_id,dept_name,emp_id,emp_name,age,sex
FROM t_emp
RIGHT JOIN t_dept ON t_emp.dept_id = t_dept.dept_id
WHERE t_dept.dept_id = #{deptId}
</select>
</mapper>
4.2、分步查询
测试程序：
package star.light.test;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import star.light.mapper.DeptMapper;
import star.light.pojo.Department;
import star.light.util.SqlSessionUtil;
public class ResultMapTest {
@Test
public void getDeptAndEmpByStep(){
SqlSession sqlSession = SqlSessionUtil.getSqlSession();
DeptMapper mapper = sqlSession.getMapper(DeptMapper.class);
Department department = mapper.getDeptAndEmpByStepOne(1);
System.out.println(department);
}
}
DeptMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Department;
public interface DeptMapper {
Department getDeptAndEmpByStepOne(@Param("deptId") Integer deptId); //通过分步查询查询部门以及部门中的员工信息的第一步
}
DeptMapper.xml 配置文件：
<?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="star.light.mapper.DeptMapper">
<resultMap id="deptAndEmpResultMapOne" type="Department">
<id column="dept_id" property="deptId"></id>
<result column="dept_name" property="deptName"></result>
<!--
collection处理一对多映射关系（处理集合类型的属性）
property：设置需要处理映射关系的属性的属性名
select：设置分步查询的sql的唯一标识
column：将查询出的某个字段作为分步查询的sql的条件
-->
<collection property="employees"
select="star.light.mapper.EmpMapper.getDeptAndEmpByStepTwo"
column="dept_id">
</collection>
</resultMap>
<!-- Department getDeptAndEmpByStepOne(@Param("deptId") Integer deptId); -->
<select id="getDeptAndEmpByStepOne" resultMap="deptAndEmpResultMapOne">
SELECT dept_id,dept_name FROM t_dept WHERE dept_id = #{deptId}
</select>
</mapper>
EmpMapper 接口：
package star.light.mapper;
import org.apache.ibatis.annotations.Param;
import star.light.pojo.Employee;
import java.util.List;
public interface EmpMapper {
List<Employee> getDeptAndEmpByStepTwo(@Param("deptId") Integer deptId); // 通过分步查询查询部门以及部门中的员工信息的第二步
}
EmpMapper.xml 配置文件：
<?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="star.light.mapper.EmpMapper">
<resultMap id="deptAndEmpResultMapTwo" type="Employee">
<id column="emp_id" property="empId"></id>
<result column="emp_name" property="empName"></result>
</resultMap>
<!-- List<Employee> getDeptAndEmpByStepTwo(@Param("deptId") Integer deptId); -->
<select id="getDeptAndEmpByStepTwo" resultMap="deptAndEmpResultMapTwo">
select emp_id,emp_name,age,sex,dept_id from t_emp where dept_id = #{deptId}
</select>
</mapper>