<select id="count" resultType="int">
        select count(id) from t_paper as p
        LEFT JOIN  t_type as t
        ON
        p.type_id=t.id
   </select>

   <resultMap id="paperResult" type="Paper">
        <!-- column:數(shù)據(jù)庫字段名 property:實體的屬(變量)名 -->
        <result column="id" property="id"/> 
        <result column="title" property="title"/>
        <result column="type_id" property="typeId"/>
        <result column="paper_summary" property="paperSummary"/>
        <result column="paper_path" property="paperPath"/>
    </resultMap>
    <select id="selectPaperListByCondition" resultMap="paperResult">
           SELECT
              p.*, t.type_name from t_paper as p
           LEFT JOIN
              t_type as t
           ON
              p.type_id=t.id
           WHERE
              title='' and type_name=''
            <where>
               <if test="title != null and title != ''">
                   and title like '%${title}%'
               </if>
                <if test="typeName != null and typeName != ''">
                    and type_name=#{typeName}
                </if>
            </where>
           limit #{start},#{size}
    </select>