Oracle Listagg函数返回null

Question

对于所有结果，good_name列为null。查询中出现什么问题？

select fp.id,
   listagg(fpg.name, ',') within group(order by fpg.name) good_name
from fp_place_goods fppg join 
   fp_places fp on fppg.place_id = fp.id join
   fp_goods fpg on fppg.good_id = fpg.id
GROUP BY fp.id

however query below works

select fp.id,
   listagg(fpg.id, ',') within group(order by fpg.id) good_ids
from fp_place_goods fppg join 
   fp_places fp on fppg.place_id = fp.id join
   fp_goods fpg on fppg.good_id = fpg.id
GROUP BY fp.id




select fp.id, fpg.name from fp_places fp join
      fp_place_goods fppg on fp.id = fppg.place_id join
      fp_goods fpg on fpg.id = fppg.good_id 

返回图像中的结果

Answer 1

之所以发生这种情况，是因为good_name是nvarchar，而to_char（fpg.name）解决了它。