src/main/resources/mybatis/mapper/UserMapper.xml

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<?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.registrationmanagementsystem.mapper.UserMapper">
    <!--
        resultType(输出类型): 输出简单类型,int,string,实体类
            1.resultType可以指定将查询结果映射为pojo，但需要pojo的属性名和sql查询的列名一致方可映射成功。
        resultMap:

         parameterType(输入类型):
            1.使用#{}占位符，或者${}进行sql拼接。
            2.Mybatis使用ognl表达式解析对象字段的值，#{}或者${}括号中的值为pojo属性名称。
    -->

    <select id="queryUserList" resultType="User">
        select * from user
    </select>
    <select id="queryUserById" resultType="User">
        select * from user where id=#{id}
    </select>
    <insert id="addUser">
        insert into user(username,password) values(#{username},#{password})
    </insert>

    <update id="updateUser">
        update user set username = #{username},password = #{password} where id = #{id}
    </update>
    <delete id="deleteUser">
        delete from user where id = #{id}
    </delete>
</mapper>