src/main/resources/mapper/UserMapper.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.example.g8backend.mapper.UserMapper">
    <select id="getUserByName" resultType="com.example.g8backend.entity.User">
        SELECT * FROM users WHERE user_name = #{userName}
    </select>
    <select id="getUserByEmail" resultType="com.example.g8backend.entity.User">
        SELECT * FROM users WHERE email = #{email}
    </select>
</mapper>