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.myproject.mapper.UserMapper">
    <!-- 根据用户名查找用户 -->
    <select id="selectByUsername" parameterType="string" resultType="com.example.myproject.entity.User">
        SELECT * FROM user WHERE username = #{username}
    </select>
    <!-- 根据用户名和密码查找用户 -->
    <select id="selectByUsernameAndPassword" parameterType="map" resultType="com.example.myproject.entity.User">
        SELECT * FROM user WHERE username = #{username} AND password = #{password}
    </select>
    <!-- 根据邮箱查找用户 -->
    <select id="selectByEmail" parameterType="string" resultType="com.example.myproject.entity.User">
        SELECT * FROM user WHERE email = #{email}
    </select>
    <!-- 根据用户名包含查找用户 -->
    <select id="selectByUsernameContaining" parameterType="string" resultType="com.example.myproject.entity.User">
        SELECT * FROM user WHERE username LIKE CONCAT('%', #{name}, '%')
    </select>
</mapper>