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.demo.dao.DemoDao">
    <select></select>
    <insert></insert>
    <update></update>
    <delete></delete>
</mapper>