IPage分页总数的sql是怎么来的，为啥分页总数total和我的数据总量不一致

1. 坑： 为啥我分页查询出来的数据总量和分页总数不一致

很简单的分页查询再现：

 public PaginationResultDto<EmergencyFileResultDto> queryTaskFiles(PagingQueryDto<EmergencyQueryDto> req) {
        EmergencyQueryDto params = req.getParams();
        if (params == null) {
            params = new EmergencyQueryDto();
        }
        IPage<EmergencyFileResultDto> page = new Page<>(req.getPage(), req.getLimit());
        page = airlineApplyManager.queryTaskFiles(params, page);
        return PaginationResultDto.success(page.getRecords(), page.getTotal());
    }

 <select id="queryTaskFiles" resultType="com.nimbus.lowaltitude.dto.airline.EmergencyFileResultDto">
        select
        afef.*
        from airline_apply aa
        left join airline_flight_execute afe on aa.id = afe.apply_id
        left join airline_flight_execute_file afef on afe.id = afef.flight_execute_id
        <where>
            <if test="queryDto.demandApplyId != null and queryDto.demandApplyId != ''">
                aa.sz_happy_id = #{queryDto.demandApplyId}
            </if>
        </where>
        order by afef.take_time desc
    </select>
       

入参:

{
  "limit": 10,
  "page": 1,
  "params": {
    "demandApplyId": "961"
  }
}

结果：我sql查询出的数据总量明明是19个，为啥total是1！！

难道不应该是

为啥？？？

2. 原因分析

当查询条件只与主表有关系时候，查询总数不会关联子表，要想实现上述效果，必须在where条件中涉及子表，或者在select 后加 distinct

3. 问题解决

 <select id="queryTaskFiles" resultType="com.nimbus.lowaltitude.dto.airline.EmergencyFileResultDto">
        select
        afef.*
        from airline_apply aa
        left join airline_flight_execute afe on aa.id = afe.apply_id
        left join airline_flight_execute_file afef on afe.id = afef.flight_execute_id
        <where>
            <if test="queryDto.demandApplyId != null and queryDto.demandApplyId != ''">
                aa.sz_happy_id = #{queryDto.demandApplyId} and afef.model_status = 1
            </if>
        </where>
        order by afef.take_time desc
    </select>