Oracle上的Subquerys

Question

我有这个问题......

 select 
  (select  
    To_Char(
       REPLACE (
         REPLACE(
           REPLACE(
             xmlagg(xmlelement("a", to_char(dt_atualizacao, 'dd/mm/yyyy')) order by dt_atualizacao).getClobVal(),
           '</a><a>', ', '),
         '<a>', ''),
       '</a>', '')
     ) xx
    from (
      select  map.nr_atendimento,
              trunc(map.dt_atualizacao) dt_atualizacao
      from    material_atend_paciente map
      where   1 = 1
              and map.nr_atendimento = ecf.nr_atendimento  -- is HERE the problem
              and obter_estrutura_material(map.cd_material,'G') = 15
      group by map.nr_atendimento, trunc(map.dt_atualizacao)
    ) yy
     group by nr_atendimento, dt_atualizacao
  ) dt_execucao_mat
FROM
  tasy.hvc_envio_conta_faturamento ecf
WHERE 1=1
  AND ecf.dt_alta BETWEEN inicio_dia(:DT_INICIAL) AND fim_dia(:DT_FINAL)
;

当我执行此命令时，oracle发送错误

ORA-00904：“ECF”。“NR_ATENDIMENTO”：identificadorinválido 00904. 00000 - “％s：无效标识符”

寻求帮助