mybatis choose when的用法实现代码如下所示：

mapper.xml:

<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>

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