当我编码
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
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
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
如果有人能向我解释，我会非常感激。
答案 0 :(得分：1)
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是一个伪列，它是作为查询的最后一步，在已生成的结果集上生成的。正在对内部选择的结果应用where rownum <= 6，但是在外部选择的那一点，您没有明确的order by子句，所以{{1}的顺序将无法保证将被分配。
您可以在外部查询中重复rownum子句，这会使处理更加不愉快，或者更简单地在内部选择中移动order by：
rownum目前还不清楚你的第一个查询的结果是否仍然是正确的顺序;可能，但也许不能保证，所以你也可以订购，以确保：
select * from (select ..., rownum rownum_ from ... order by ...)
where rownum_ <= 6;
（另一种方法是针对您在select * from (select ..., rownum rownum_ from ... order by ...)
where rownum_ <= 6
order by rownum_;
中使用的dense_rank()使用case之类的分析函数，然后在外部order by中使用它限制行数，但这有点远离问题...）
答案 1 :(得分：0)
在没有order by子句的情况下执行相同查询时，Oracle不保证相同的行顺序。
答案 2 :(得分：0)
文档说：Oracle指定ROWNUM显示“Oracle从一个表或一组连接的行中选择行的顺序”。也就是说，在结果集排序之前。 Find out more。
因此，如果您想保证前n行始终是给定结果集的相同行，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
;
还有其他方法可以解决前n个问题 - 例如使用RANK或ROW_NUMBER - 但它们都依赖于内部查询。以下是使用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
;