Mybatis choose when用法实例代码

<select id="query" resulttype="map" parametertype="map">
    select 
      <choose>
        <when test="cityid == '00' ">
            a.city_id as cityid,
        </when>
        <otherwise>
          <choose>
            <when test="cityid == '0001' and statsdimension==1">
              a.level1_maintain_unit_id as cityid,
            </when>
            <otherwise>
              a.county_id as cityid,
            </otherwise>
          </choose>
         </otherwise>
     </choose>
          sum(onunum) as onunum, 
          sum(ontnum) as ontnum
      from new_olt_upopt_sp_month_${tabledate} a
      where 1 = 1
        <if test="cityid == '0001' and statsdimension==1">
        and a.city_id = '0001'
        </if>
        <![cdata[and a.gather_time >= ${startdate}]]>
        <![cdata[and a.gather_time <= ${enddate}]]>  
         group by
    <choose>
        <when test="cityid == '00' ">
            a.city_id
        </when>
        <otherwise>
          <choose>
            <when test="cityid == '0001' and statsdimension==1">
              a.level1_maintain_unit_id
            </when>
            <otherwise>
              a.county_id
              having a.county_id in 
                (select city_id from tab_city 
                  where city_id= #{cityid} or parent_id=#{cityid})
            </otherwise>
          </choose>
         </otherwise>
     </choose>      
  </select>