StudentMapper.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.meishu.mapper.StudentMapper">

    <select id="students" parameterType="string" resultType="com.meishu.model.StudentDO">
        SELECT
        t.id,
        t.user_name,
        t.id_card,
        t.company_name
        FROM
        student t
        WHERE
        t.delete_date IS NULL
        <if test="userName != null and userName != ''">
            and t.user_name like concat('%',#{userName} ,'%')
        </if>
    </select>


</mapper>