Oracle关联查询问题？

查询结果如下列表：
------------------------------------
  c1705_datetime  c0003_stcode c0007_pcode c0001_item_code  avg
1 2013-05-19 00:00                                                                 2 2013-05-19 01:00            
3 2013-05-19 02:00            
4 2013-05-19 03:00            
5 2013-05-19 04:00            
6 2013-05-19 05:00            
7 2013-05-19 06:00           
8 2013-05-19 07:00            
9 2013-05-19 08:00            
10 2013-05-19 09:00            
11 2013-05-19 10:00 370102     218          101    
12 2013-05-19 11:00 370102     218          101       0.091    
13 2013-05-19 12:00 370102     218          101       0.017                       
14 2013-05-19 13:00 370102     218          101       0.036                        
15 2013-05-19 14:00 370102     218          101       0.047                         
16 2013-05-19 15:00 370102     218          101       0.044                       
17 2013-05-19 16:00 370102     218          101       0.047                       
18 2013-05-19 17:00 370102     218          101       0.045                       
19 2013-05-19 18:00 370102     218          101       0.045                       
20 2013-05-19 19:00 370102     218          101       0.069                       
21 2013-05-19 20:00 370102     218          101       0.051                       
22 2013-05-19 21:00 370102     218          101       0.049                       
23 2013-05-19 22:00 370102     218          101       0.082                       
24 2013-05-19 23:00 370102     218          101       0.082    
---------------------------------------------
我实现的是和时间表关联，如果没数据也显示时间列。但是我想没数据时，c0003_stcode c0007_pcode c0001_item_code也显示出来，avg显示为空，就象如下样式：
         c1705_datetime      c0003_stcode c0007_pcode c0001_item_code  avg
11 2013-05-19 10:00 370102     218          101    
请问关联SQL语句怎么写？