为何从数据库里读数据时，只循环最后一条记录呢

          while(rs.next()){
              petItem pi=new petItem(); 
              pi.petId = rs.getString(1); 
              pi.petName = rs.getString(2); 
              pi.petType = rs.getString(3); 
              pi.petPrice = rs.getInt(4); 
              pi.petRemark = rs.getString(5); 
           
              al.add(pi); 
          }