Mybatis 采坑记录--set标签的使用

 <!--根据poi_info表的id和city_id更新flag_hinterland_flows的poi_id和city_id-->
    <select id="selectPoiAndCityId" parameterType="java.lang.Long" resultType="com.wormpex.gs.stat.service.dao.entity.baseinfo.PoiAndCityId">
        select n.id as poiId,n.city_id as cityId,n.code as code from poi_info n inner join flag_hinterland_flows m   
/*1用inner join，只返回满足匹配条件的数据，减少数据库io次数*/
        on m.flag_code=n.code
        <where>
            <if test="id != null">
           n.id<![CDATA[<=]]>#{id,jdbcType=BIGINT}
            </if>
        </where>
    </select>

    <update id="updatePoiAndCityId" parameterType="com.wormpex.gs.stat.service.dao.entity.baseinfo.PoiAndCityId"  >
        update flag_hinterland_flows
        <set>
            poi_id=#{poiId,jdbcType=BIGINT},
            <if test="cityId != null">
                city_id=#{cityId,jdbcType=BIGINT},
            </if>
        </set>  /*2set标签可以自动忽略if标签中多余的逗号，但是，对于if标签里面再嵌套一层if的时候，set标签就不能自动忽略了*/
        where     /*3where放到set标签外边*/
        flag_code=#{code,jdbcType=VARCHAR}
    </update>