oracle - rownum 混淆结果

Question

当我编码时

select 
    row_.*, rownum rownum_ 
from 
   (select 
       topic0_.id as id6_, topic0_.title as title6_,  
       topic0_.publish_author_id as publish3_6_, topic0_.reply_number as reply4_6_, 
       topic0_.read_number as read5_6_, topic0_.publish_author_name as publish6_6_, 
       topic0_.publish_time as publish7_6_, topic0_.last_reply_time as last8_6_, 
       topic0_.last_reply_name as last9_6_, topic0_.main_text as main10_6_, topic0_.FORUM_ID as FORUM11_6_ 
    from topic topic0_ 
    where topic0_.FORUM_ID='16F37E59FE494AC9B17A2340387335EF' 
    order by 
        case when topic0_.last_reply_time is not null then topic0_.last_reply_time 
        else  topic0_.publish_time end desc
    ) row_;

结果：

    ID6_    TITLE6_ PUBLISH3_6_ REPLY4_6_   READ5_6_    PUBLISH6_6_ PUBLISH7_6_ LAST8_6_    LAST9_6_    MAIN10_6_   FORUM11_6_  ROWNUM_
1   402840713e108ea4013e1090c95c0001    trytr   2   2   0   ss  2013-4-16 9:58:44   2013-4-16 9:59:21   ss  fdsfds  16F37E59FE494AC9B17A2340387335EF    1
2   402840713e108ea4013e1090127e0000    trytr   2   0   0   ss  2013-4-16 9:57:57           ytrytr  16F37E59FE494AC9B17A2340387335EF    2
3   402840713e0d3616013e0d3618c20000    cde0    2   0   0   ss  2013-4-15 18:20:49          abc0    16F37E59FE494AC9B17A2340387335EF    3
4   402840713e0d3616013e0d3618da0063    cde99   2   0   0   ss  2013-4-15 18:20:49          abc99   16F37E59FE494AC9B17A2340387335EF    4
5   402840713e0d3616013e0d3618da0062    cde98   2   0   0   ss  2013-4-15 18:20:49          abc98   16F37E59FE494AC9B17A2340387335EF    5
6   402840713e0d3616013e0d3618da0061    cde97   2   0   0   ss  2013-4-15 18:20:49          abc97   16F37E59FE494AC9B17A2340387335EF    6
7   402840713e0d3616013e0d3618da0060    cde96   2   0   0   ss  2013-4-15 18:20:49          abc96   16F37E59FE494AC9B17A2340387335EF    7
8   402840713e0d3616013e0d3618da005f    cde95   2   0   0   ss  2013-4-15 18:20:49          abc95   16F37E59FE494AC9B17A2340387335EF    8
9   402840713e0d3616013e0d3618da005e    cde94   2   0   0   ss  2013-4-15 18:20:49          abc94   16F37E59FE494AC9B17A2340387335EF    9
10  402840713e0d3616013e0d3618da005d    cde93   2   0   0   ss  2013-4-15 18:20:49          abc93   16F37E59FE494AC9B17A2340387335EF    10
11  402840713e0d3616013e0d3618da005c    cde92   2   0   0   ss  2013-4-15 18:20:49          abc92   16F37E59FE494AC9B17A2340387335EF    11
12  402840713e0d3616013e0d3618da005b    cde91   2   0   0   ss  2013-4-15 18:20:49          abc91   16F37E59FE494AC9B17A2340387335EF    12
13  402840713e0d3616013e0d3618d9005a    cde90   2   0   0   ss  2013-4-15 18:20:49          abc90   16F37E59FE494AC9B17A2340387335EF    13
14  402840713e0d3616013e0d3618d90059    cde89   2   0   0   ss  2013-4-15 18:20:49          abc89   16F37E59FE494AC9B17A2340387335EF    14
15  402840713e0d3616013e0d3618d90058    cde88   2   0   0   ss  2013-4-15 18:20:49          abc88   16F37E59FE494AC9B17A2340387335EF    15
16  402840713e0d3616013e0d3618d90057    cde87   2   0   0   ss  2013-4-15 18:20:49          abc87   16F37E59FE494AC9B17A2340387335EF    16
17  402840713e0d3616013e0d3618d90056    cde86   2   0   0   ss  2013-4-15 18:20:49          abc86   16F37E59FE494AC9B17A2340387335EF    17
18  402840713e0d3616013e0d3618d90055    cde85   2   0   0   ss  2013-4-15 18:20:49          abc85   16F37E59FE494AC9B17A2340387335EF    18
19  402840713e0d3616013e0d3618d90054    cde84   2   0   0   ss  2013-4-15 18:20:49          abc84   16F37E59FE494AC9B17A2340387335EF    19
20  402840713e0d3616013e0d3618d90053    cde83   2   0   0   ss  2013-4-15 18:20:49          abc83   16F37E59FE494AC9B17A2340387335EF    20
21  402840713e0d3616013e0d3618d90052    cde82   2   0   0   ss  2013-4-15 18:20:49          abc82   16F37E59FE494AC9B17A2340387335EF    21
22  402840713e0d3616013e0d3618d90051    cde81   2   0   0   ss  2013-4-15 18:20:49          abc81   16F37E59FE494AC9B17A2340387335EF    22
23  402840713e0d3616013e0d3618d80050    cde80   2   0   0   ss  2013-4-15 18:20:49          abc80   16F37E59FE494AC9B17A2340387335EF    23
24  402840713e0d3616013e0d3618d8004f    cde79   2   0   0   ss  2013-4-15 18:20:49          abc79   16F37E59FE494AC9B17A2340387335EF    24
25  402840713e0d3616013e0d3618d8004e    cde78   2   0   0   ss  2013-4-15 18:20:49          abc78   16F37E59FE494AC9B17A2340387335EF    25
26  402840713e0d3616013e0d3618d8004d    cde77   2   0   0   ss  2013-4-15 18:20:49          abc77   16F37E59FE494AC9B17A2340387335EF    26
27  402840713e0d3616013e0d3618d8004c    cde76   2   0   0   ss  2013-4-15 18:20:49          abc76   16F37E59FE494AC9B17A2340387335EF    27
28  402840713e0d3616013e0d3618d8004b    cde75   2   0   0   ss  2013-4-15 18:20:49          abc75   16F37E59FE494AC9B17A2340387335EF    28
29  402840713e0d3616013e0d3618d8004a    cde74   2   0   0   ss  2013-4-15 18:20:49          abc74   16F37E59FE494AC9B17A2340387335EF    29
30  402840713e0d3616013e0d3618d80049    cde73   2   0   0   ss  2013-4-15 18:20:49          abc73   16F37E59FE494AC9B17A2340387335EF    30
31  402840713e0d3616013e0d3618d80048    cde72   2   0   0   ss  2013-4-15 18:20:49          abc72   16F37E59FE494AC9B17A2340387335EF    31
32  402840713e0d3616013e0d3618d70047    cde71   2   0   0   ss  2013-4-15 18:20:49          abc71   16F37E59FE494AC9B17A2340387335EF    32
33  402840713e0d3616013e0d3618d70046    cde70   2   0   0   ss  2013-4-15 18:20:49          abc70   16F37E59FE494AC9B17A2340387335EF    33
34  402840713e0d3616013e0d3618d70045    cde69   2   0   0   ss  2013-4-15 18:20:49          abc69   16F37E59FE494AC9B17A2340387335EF    34
35  402840713e0d3616013e0d3618d70044    cde68   2   0   0   ss  2013-4-15 18:20:49          abc68   16F37E59FE494AC9B17A2340387335EF    35
36  402840713e0d3616013e0d3618d70043    cde67   2   0   0   ss  2013-4-15 18:20:49          abc67   16F37E59FE494AC9B17A2340387335EF    36
37  402840713e0d3616013e0d3618d70042    cde66   2   0   0   ss  2013-4-15 18:20:49          abc66   16F37E59FE494AC9B17A2340387335EF    37
38  402840713e0d3616013e0d3618d70041    cde65   2   0   0   ss  2013-4-15 18:20:49          abc65   16F37E59FE494AC9B17A2340387335EF    38
39  402840713e0d3616013e0d3618d70040    cde64   2   0   0   ss  2013-4-15 18:20:49          abc64   16F37E59FE494AC9B17A2340387335EF    39
40  402840713e0d3616013e0d3618d7003f    cde63   2   0   0   ss  2013-4-15 18:20:49          abc63   16F37E59FE494AC9B17A2340387335EF    40
41  402840713e0d3616013e0d3618d7003e    cde62   2   0   0   ss  2013-4-15 18:20:49          abc62   16F37E59FE494AC9B17A2340387335EF    41
42  402840713e0d3616013e0d3618d6003d    cde61   2   0   0   ss  2013-4-15 18:20:49          abc61   16F37E59FE494AC9B17A2340387335EF    42
43  402840713e0d3616013e0d3618d6003c    cde60   2   0   0   ss  2013-4-15 18:20:49          abc60   16F37E59FE494AC9B17A2340387335EF    43
44  402840713e0d3616013e0d3618d6003b    cde59   2   0   0   ss  2013-4-15 18:20:49          abc59   16F37E59FE494AC9B17A2340387335EF    44
45  402840713e0d3616013e0d3618d6003a    cde58   2   0   0   ss  2013-4-15 18:20:49          abc58   16F37E59FE494AC9B17A2340387335EF    45
46  402840713e0d3616013e0d3618d60039    cde57   2   0   0   ss  2013-4-15 18:20:49          abc57   16F37E59FE494AC9B17A2340387335EF    46
47  402840713e0d3616013e0d3618d60038    cde56   2   0   0   ss  2013-4-15 18:20:49          abc56   16F37E59FE494AC9B17A2340387335EF    47
48  402840713e0d3616013e0d3618d60037    cde55   2   0   0   ss  2013-4-15 18:20:49          abc55   16F37E59FE494AC9B17A2340387335EF    48
49  402840713e0d3616013e0d3618d60036    cde54   2   0   0   ss  2013-4-15 18:20:49          abc54   16F37E59FE494AC9B17A2340387335EF    49
50  402840713e0d3616013e0d3618d60035    cde53   2   0   0   ss  2013-4-15 18:20:49          abc53   16F37E59FE494AC9B17A2340387335EF    50
51  402840713e0d3616013e0d3618d50034    cde52   2   0   0   ss  2013-4-15 18:20:49          abc52   16F37E59FE494AC9B17A2340387335EF    51
52  402840713e0d3616013e0d3618d50033    cde51   2   0   0   ss  2013-4-15 18:20:49          abc51   16F37E59FE494AC9B17A2340387335EF    52
53  402840713e0d3616013e0d3618d50032    cde50   2   0   0   ss  2013-4-15 18:20:49          abc50   16F37E59FE494AC9B17A2340387335EF    53
54  402840713e0d3616013e0d3618d50031    cde49   2   0   0   ss  2013-4-15 18:20:49          abc49   16F37E59FE494AC9B17A2340387335EF    54
55  402840713e0d3616013e0d3618d50030    cde48   2   0   0   ss  2013-4-15 18:20:49          abc48   16F37E59FE494AC9B17A2340387335EF    55
56  402840713e0d3616013e0d3618d5002f    cde47   2   0   0   ss  2013-4-15 18:20:49          abc47   16F37E59FE494AC9B17A2340387335EF    56
57  402840713e0d3616013e0d3618d5002e    cde46   2   0   0   ss  2013-4-15 18:20:49          abc46   16F37E59FE494AC9B17A2340387335EF    57
58  402840713e0d3616013e0d3618d5002d    cde45   2   0   0   ss  2013-4-15 18:20:49          abc45   16F37E59FE494AC9B17A2340387335EF    58
59  402840713e0d3616013e0d3618d5002c    cde44   2   0   0   ss  2013-4-15 18:20:49          abc44   16F37E59FE494AC9B17A2340387335EF    59
60  402840713e0d3616013e0d3618d5002b    cde43   2   0   0   ss  2013-4-15 18:20:49          abc43   16F37E59FE494AC9B17A2340387335EF    60
61  402840713e0d3616013e0d3618d5002a    cde42   2   0   0   ss  2013-4-15 18:20:49          abc42   16F37E59FE494AC9B17A2340387335EF    61
62  402840713e0d3616013e0d3618d40029    cde41   2   0   0   ss  2013-4-15 18:20:49          abc41   16F37E59FE494AC9B17A2340387335EF    62
63  402840713e0d3616013e0d3618d40028    cde40   2   0   0   ss  2013-4-15 18:20:49          abc40   16F37E59FE494AC9B17A2340387335EF    63
64  402840713e0d3616013e0d3618d40027    cde39   2   0   0   ss  2013-4-15 18:20:49          abc39   16F37E59FE494AC9B17A2340387335EF    64
65  402840713e0d3616013e0d3618d40026    cde38   2   0   0   ss  2013-4-15 18:20:49          abc38   16F37E59FE494AC9B17A2340387335EF    65
66  402840713e0d3616013e0d3618d40025    cde37   2   0   0   ss  2013-4-15 18:20:49          abc37   16F37E59FE494AC9B17A2340387335EF    66
67  402840713e0d3616013e0d3618d40024    cde36   2   0   0   ss  2013-4-15 18:20:49          abc36   16F37E59FE494AC9B17A2340387335EF    67
68  402840713e0d3616013e0d3618d40023    cde35   2   0   0   ss  2013-4-15 18:20:49          abc35   16F37E59FE494AC9B17A2340387335EF    68
69  402840713e0d3616013e0d3618d40022    cde34   2   0   0   ss  2013-4-15 18:20:49          abc34   16F37E59FE494AC9B17A2340387335EF    69
70  402840713e0d3616013e0d3618d30021    cde33   2   0   0   ss  2013-4-15 18:20:49          abc33   16F37E59FE494AC9B17A2340387335EF    70
71  402840713e0d3616013e0d3618d30020    cde32   2   0   0   ss  2013-4-15 18:20:49          abc32   16F37E59FE494AC9B17A2340387335EF    71
72  402840713e0d3616013e0d3618d3001f    cde31   2   0   0   ss  2013-4-15 18:20:49          abc31   16F37E59FE494AC9B17A2340387335EF    72
73  402840713e0d3616013e0d3618d3001e    cde30   2   0   0   ss  2013-4-15 18:20:49          abc30   16F37E59FE494AC9B17A2340387335EF    73
74  402840713e0d3616013e0d3618d3001d    cde29   2   0   0   ss  2013-4-15 18:20:49          abc29   16F37E59FE494AC9B17A2340387335EF    74
75  402840713e0d3616013e0d3618d3001c    cde28   2   0   0   ss  2013-4-15 18:20:49          abc28   16F37E59FE494AC9B17A2340387335EF    75
76  402840713e0d3616013e0d3618d3001b    cde27   2   0   0   ss  2013-4-15 18:20:49          abc27   16F37E59FE494AC9B17A2340387335EF    76
77  402840713e0d3616013e0d3618d3001a    cde26   2   0   0   ss  2013-4-15 18:20:49          abc26   16F37E59FE494AC9B17A2340387335EF    77
78  402840713e0d3616013e0d3618d30019    cde25   2   0   0   ss  2013-4-15 18:20:49          abc25   16F37E59FE494AC9B17A2340387335EF    78
79  402840713e0d3616013e0d3618d30018    cde24   2   0   0   ss  2013-4-15 18:20:49          abc24   16F37E59FE494AC9B17A2340387335EF    79
80  402840713e0d3616013e0d3618d20017    cde23   2   0   0   ss  2013-4-15 18:20:49          abc23   16F37E59FE494AC9B17A2340387335EF    80
81  402840713e0d3616013e0d3618d20016    cde22   2   0   0   ss  2013-4-15 18:20:49          abc22   16F37E59FE494AC9B17A2340387335EF    81
82  402840713e0d3616013e0d3618d20015    cde21   2   0   0   ss  2013-4-15 18:20:49          abc21   16F37E59FE494AC9B17A2340387335EF    82
83  402840713e0d3616013e0d3618d20014    cde20   2   0   0   ss  2013-4-15 18:20:49          abc20   16F37E59FE494AC9B17A2340387335EF    83
84  402840713e0d3616013e0d3618d20013    cde19   2   0   0   ss  2013-4-15 18:20:49          abc19   16F37E59FE494AC9B17A2340387335EF    84
85  402840713e0d3616013e0d3618d20012    cde18   2   0   0   ss  2013-4-15 18:20:49          abc18   16F37E59FE494AC9B17A2340387335EF    85
86  402840713e0d3616013e0d3618d20011    cde17   2   0   0   ss  2013-4-15 18:20:49          abc17   16F37E59FE494AC9B17A2340387335EF    86
87  402840713e0d3616013e0d3618d20010    cde16   2   0   0   ss  2013-4-15 18:20:49          abc16   16F37E59FE494AC9B17A2340387335EF    87
88  402840713e0d3616013e0d3618d0000f    cde15   2   0   0   ss  2013-4-15 18:20:49          abc15   16F37E59FE494AC9B17A2340387335EF    88
89  402840713e0d3616013e0d3618cf000e    cde14   2   0   0   ss  2013-4-15 18:20:49          abc14   16F37E59FE494AC9B17A2340387335EF    89
90  402840713e0d3616013e0d3618cf000d    cde13   2   0   0   ss  2013-4-15 18:20:49          abc13   16F37E59FE494AC9B17A2340387335EF    90
91  402840713e0d3616013e0d3618cf000c    cde12   2   0   0   ss  2013-4-15 18:20:49          abc12   16F37E59FE494AC9B17A2340387335EF    91
92  402840713e0d3616013e0d3618cf000b    cde11   2   0   0   ss  2013-4-15 18:20:49          abc11   16F37E59FE494AC9B17A2340387335EF    92
93  402840713e0d3616013e0d3618cf000a    cde10   2   0   0   ss  2013-4-15 18:20:49          abc10   16F37E59FE494AC9B17A2340387335EF    93
94  402840713e0d3616013e0d3618ce0009    cde9    2   0   0   ss  2013-4-15 18:20:49          abc9    16F37E59FE494AC9B17A2340387335EF    94
95  402840713e0d3616013e0d3618ce0008    cde8    2   0   0   ss  2013-4-15 18:20:49          abc8    16F37E59FE494AC9B17A2340387335EF    95
96  402840713e0d3616013e0d3618ce0007    cde7    2   0   0   ss  2013-4-15 18:20:49          abc7    16F37E59FE494AC9B17A2340387335EF    96
97  402840713e0d3616013e0d3618ce0006    cde6    2   0   0   ss  2013-4-15 18:20:49          abc6    16F37E59FE494AC9B17A2340387335EF    97
98  402840713e0d3616013e0d3618ce0005    cde5    2   0   0   ss  2013-4-15 18:20:49          abc5    16F37E59FE494AC9B17A2340387335EF    98
99  402840713e0d3616013e0d3618ce0004    cde4    2   0   0   ss  2013-4-15 18:20:49          abc4    16F37E59FE494AC9B17A2340387335EF    99
100 402840713e0d3616013e0d3618ce0003    cde3    2   0   0   ss  2013-4-15 18:20:49          abc3    16F37E59FE494AC9B17A2340387335EF    100
101 402840713e0d3616013e0d3618ce0002    cde2    2   0   0   ss  2013-4-15 18:20:49          abc2    16F37E59FE494AC9B17A2340387335EF    101
102 402840713e0d3616013e0d3618cd0001    cde1    2   0   0   ss  2013-4-15 18:20:49          abc1    16F37E59FE494AC9B17A2340387335EF    102
103 402840713e0cb39c013e0cb41c040000    dfsdf   2   1   0   ss  2013-4-15 15:58:50          sdfsdfsdf   16F37E59FE494AC9B17A2340387335EF    103
104 402840713e0c9424013e0c94a8c30000    fffff   2   1   0   ss  2013-4-15 15:24:29          dgfdgfdg    16F37E59FE494AC9B17A2340387335EF    104
105 402840713e0c8e00013e0c8f1d190000    asf 2   2   0   ss  2013-4-15 15:18:25          dsfds   16F37E59FE494AC9B17A2340387335EF    105
106 402840713e0c80ce013e0c8158630000    ccc 2   1   0   ss  2013-4-15 15:03:23          dfsd    16F37E59FE494AC9B17A2340387335EF    106
107 402840713e0c5a97013e0c5b0c200000    hhhhh   2   2   0   ss  2013-4-15 14:21:33          fds 16F37E59FE494AC9B17A2340387335EF    107
108 402840713e0c58cd013e0c592b550000    hff 2   0   0   ss  2013-4-15 14:19:30          sdfs    16F37E59FE494AC9B17A2340387335EF    108
109 402840713e0c272d013e0c2e12c40000    gsfsdf  2   0   0   ss  2013-4-15 13:32:26          fdsfds  16F37E59FE494AC9B17A2340387335EF    109
110 402840713e0c25ef013e0c265f720000    fdsf    2   0   0   ss  2013-4-15 13:24:01          fsdfsdf 16F37E59FE494AC9B17A2340387335EF    110
111 402840713e0c2237013e0c228d4b0000    fdsf    2   0   0   ss  2013-4-15 13:19:51          sdfs    16F37E59FE494AC9B17A2340387335EF    111
112 402840713e0c1cc9013e0c1d0dc30000    fsdf    2   0   0   ss  2013-4-15 13:13:50          sdfdsfds    16F37E59FE494AC9B17A2340387335EF    112
113 402840713e0c1be8013e0c1c33bf0000    fsfds   2   0   0   ss  2013-4-15 13:12:54          fdsfsd  16F37E59FE494AC9B17A2340387335EF    113
114 402840713e0c1b0b013e0c1b72320000    fsfsd   2   0   0   ss  2013-4-15 13:12:05          fsdfsd  16F37E59FE494AC9B17A2340387335EF    114
115 402840713e0c19a9013e0c19f49b0000    GDFG    2   0   0   ss  2013-4-15 13:10:27          FDGDFGDF    16F37E59FE494AC9B17A2340387335EF    115
116 402840713e0c17c7013e0c184b200000    fdsfsd  2   0   0   ss  2013-4-15 13:08:38          fsdfsdfs    16F37E59FE494AC9B17A2340387335EF    116
117 402840713e0c0edc013e0c0f79d20000    fsdfds  2   0   0   ss  2013-4-15 12:59:00          fdsfdsfdsfd 16F37E59FE494AC9B17A2340387335EF    117
118 402840713e0bee4f013e0bef28150000    fdsfsd  2   0   0   ss  2013-4-15 12:23:42          fdsfsdf 16F37E59FE494AC9B17A2340387335EF    118
119 402840713e0b92fc013e0b9418cf0000    fdsfdsf 2   0   0   ss  2013-4-15 10:44:15          dsfdsfdsfds 16F37E59FE494AC9B17A2340387335EF    119

但是当我编码时

       select row_.*, rownum rownum_ from (select topic0_.id as id6_, topic0_.title as title6_, topic0_.publish_author_id as publish3_6_, topic0_.reply_number as reply4_6_, topic0_.read_number as read5_6_, topic0_.publish_author_name as publish6_6_, topic0_.publish_time as publish7_6_, topic0_.last_reply_time as last8_6_, topic0_.last_reply_name as last9_6_, topic0_.main_text as main10_6_, topic0_.FORUM_ID as FORUM11_6_ from topic topic0_ where topic0_.FORUM_ID='16F37E59FE494AC9B17A2340387335EF' order by case when topic0_.last_reply_time is not null then topic0_.last_reply_time else  topic0_.publish_time end desc) row_ where rownum <=6;

结果是

    ID6_    TITLE6_ PUBLISH3_6_ REPLY4_6_   READ5_6_    PUBLISH6_6_ PUBLISH7_6_ LAST8_6_    LAST9_6_    MAIN10_6_   FORUM11_6_  ROWNUM_ 
1   402840713e108ea4013e1090c95c0001    trytr   2   2   0   ss  2013-4-16 9:58:44   2013-4-16 9:59:21   ss  fdsfds  16F37E59FE494AC9B17A2340387335EF    1   
2   402840713e108ea4013e1090127e0000    trytr   2   0   0   ss  2013-4-16 9:57:57           ytrytr  16F37E59FE494AC9B17A2340387335EF    2   
3   402840713e0d3616013e0d3618c20000    cde0    2   0   0   ss  2013-4-15 18:20:49          abc0    16F37E59FE494AC9B17A2340387335EF    3   
4   402840713e0d3616013e0d3618ce0003    cde3    2   0   0   ss  2013-4-15 18:20:49          abc3    16F37E59FE494AC9B17A2340387335EF    4   
5   402840713e0d3616013e0d3618ce0002    cde2    2   0   0   ss  2013-4-15 18:20:49          abc2    16F37E59FE494AC9B17A2340387335EF    5   
6   402840713e0d3616013e0d3618cd0001    cde1    2   0   0   ss  2013-4-15 18:20:49          abc1    16F37E59FE494AC9B17A2340387335EF    6

为什么？我想要的结果是：

    ID6_    TITLE6_ PUBLISH3_6_ REPLY4_6_   READ5_6_    PUBLISH6_6_ PUBLISH7_6_ LAST8_6_    LAST9_6_    MAIN10_6_   FORUM11_6_  ROWNUM_
1   402840713e108ea4013e1090c95c0001    trytr   2   2   0   ss  2013-4-16 9:58:44   2013-4-16 9:59:21   ss  fdsfds  16F37E59FE494AC9B17A2340387335EF    1
2   402840713e108ea4013e1090127e0000    trytr   2   0   0   ss  2013-4-16 9:57:57           ytrytr  16F37E59FE494AC9B17A2340387335EF    2
3   402840713e0d3616013e0d3618c20000    cde0    2   0   0   ss  2013-4-15 18:20:49          abc0    16F37E59FE494AC9B17A2340387335EF    3
4   402840713e0d3616013e0d3618da0063    cde99   2   0   0   ss  2013-4-15 18:20:49          abc99   16F37E59FE494AC9B17A2340387335EF    4
5   402840713e0d3616013e0d3618da0062    cde98   2   0   0   ss  2013-4-15 18:20:49          abc98   16F37E59FE494AC9B17A2340387335EF    5
6   402840713e0d3616013e0d3618da0061    cde97   2   0   0   ss  2013-4-15 18:20:49          abc97   16F37E59FE494AC9B17A2340387335EF    6

如果有人可以向我解释，我将不胜感激。

score 2 · Accepted Answer

在您的第一个查询中，您有：

select row_.*, rownum rownum_ from (select ... order by ...) row_;

在第二个你有：

select row_.*, rownum rownum_ from (select ... order by ...) row_
where rownum <= 6;

rownum是作为查询的最后一步生成的伪列，在已经生成的结果集之上。where rownum <= 6正在针对内部选择的结果应用，但此时在外部选择中您没有显式order by子句，因此rownum无法保证分配的顺序。

您可以order by在外部查询中重复该子句，这会使处理起来更加不愉快，或者更简单地移动rownum内部选择的内部：

select * from (select ..., rownum rownum_ from ... order by ...)
where rownum_ <= 6;

尚不清楚您的第一个查询的结果是否按正确的顺序排列；可能，但又可能无法保证，因此您也可以订购以确保：

select * from (select ..., rownum rownum_ from ... order by ...)
where rownum_ <= 6
order by rownum_;

（另一种方法是使用一个分析函数，比如你在中使用的dense_rank()，然后在外部使用它来限制行数，但这有点远离问题......）caseorder bywhere

score 1 · Accepted Answer

1

order by在没有子句的情况下执行相同的查询时，Oracle 不保证相同的行顺序。

于 2013-04-16T06:31:00.247 回答

score 0 · Accepted Answer

文档说：ROWNUM 由 Oracle 分配以显示“Oracle 从表或一组连接行中选择行的顺序”。也就是在结果集被排序之前。了解更多。

因此，如果要保证给定结果集的前 n 行始终是相同的行，则需要对其进行预排序。

select t2.* from
   ( select t1.*, rownum as rownum_ from 
       ( select t.* from t order by t.whatever ) t1
    ) 
where rownum_  <= 6
;

还有其他解决 top-n 问题的方法——例如使用 RANK 或 ROW_NUMBER——但它们都依赖于内部查询。这是使用 ROW_NUMBER() 完成的上述解决方案。

   select t1.* from 
       ( select t.*
                 , row_number() over ( order by t.whatever )   as rownum_
         from t ) t1
  where rownum_  <= 6
 ;

oracle - rownum 混淆结果

3 回答 3

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