iHotel_student_houtai/src/main/resources/mapper/template/UsersMapper.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.template.mapper.UsersMapper">

    <select id="departmentList" resultType="java.lang.String">
        SELECT department FROM `users` GROUP BY department
    </select>
</mapper>