Oracle查询的等效Postgres查询

Question

哪个Postgres查询等同于以下Oracle查询？

select CID,
  max(cus.customer_id)  keep (dense_rank first order by decode(acct.CUS_Type,'X',4,'M',5,'F',6,'G',7,'I',5,6), start_date)  best_CUS
  from cusomer cus
    group by CID ;