关于rownum排序分页会比分析函数排序快的问题。。。

测试过程：
create table test as select * from dba_objects;
insert into test select * form dba_objects;
……
commit;

create table sort_test as
  select rownum rn,t.* from test t order by object_id;

SQL> select count(*) from sort_test;

  COUNT(*)
----------
    842752

create or replace procedure sp_test is
  num1 number;
  num2 number;
begin
  runstats_pgk.rs_start;
  for i in 1..100 loop
    select count(*) into num1 from
    (
       select * from (
       select rownum countnum,t.* from (
       select * from sort_test order by object_id,rn) t where rownum<=50
       ) where countnum>0
    );
  end loop;
  runstats_pgk.rs_middle;
  for i in 1..100 loop
    select count(*) into num2 from (
       select * from (
       select row_number() over(order by object_id,rn) countnum,t.* from sort_test t)
       where countnum>0 and countnum<=50
    );
  end loop;
  runstats_pgk.rs_stop;
end sp_test;

以下是测试的结果：
SQL> exec sp_test;
run1 ran in 21286 hsecs
run2 ran in 16932 hsecs
run1 ran in 125.71% if the time

Name                                Run1        Run2      Diff
LATCH.simulator lru latch              1         0        -1
STAT...change write time               1         0        -1
STAT...free buffer requested           4         5         1
LATCH.job_queue_processes para         4         2        -2
STAT...cleanout - number of kt         3         5         2
STAT...consistent gets - exami         3         5         2
STAT...consistent gets         1,093,003 1,093,005         2
STAT...active txn count during         3         5         2
STAT...calls to kcmgcs                 3         5         2
LATCH.row cache objects              149       152         3
LATCH.row cache enqueue latch        144       148         4
STAT...consistent changes            509       515         6
STAT...db block gets                 519       525         6
STAT...db block changes            1,018     1,025         7
STAT...session logical reads   1,093,522 1,093,530         8
LATCH.dml lock allocation              5        19        14
LATCH.hash table column usage          0        14        14
LATCH.lgwr LWN SCN                    70        56       -14
LATCH.mostly latch-free SCN           70        56       -14
LATCH.session allocation              52        38       -14
LATCH.redo allocation                580       594        14
LATCH.active checkpoint queue         70        55       -15
LATCH.session timer                   71        56       -15
LATCH.enqueue hash chains            254       236       -18
LATCH.undo global data                23        44        21
LATCH.channel operations paren       137       111       -26
LATCH.redo writing                   220       180       -40
LATCH.enqueues                       276       223       -53
LATCH.session idle bit               170       115       -55
STAT...redo size                  64,880    64,940        60
LATCH.library cache pin alloca       112       178        66
LATCH.cache buffers chains     2,189,080 2,189,156        76
LATCH.shared pool                    282       361        79
LATCH.library cache pin              537       627        90
LATCH.messages                       511       407      -104
LATCH.simulator hash latch        69,249    69,120      -129
LATCH.library cache                  655       800       145
LATCH.SQL memory manager worka     4,556     3,885      -671
LATCH.checkpoint queue latch       6,656     5,280    -1,376
STAT...recursive cpu usage        21,291    16,933    -4,358
STAT...session pga memory max      7,916         0    -7,916

run1 latchs total versus runs -- defference and pct
Run1      Run2      Diff     Pct
2,273,958 2,271,937    -2,021       100%

PL/SQL 过程已成功完成。

SELECT count(*) from
    (
       select * from (
       select rownum countnum,t.* from (
       select * from sort_test order by object_id,rn) t where rownum<=50
       ) where countnum>0
    )

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute    100      0.00       0.00          0          0          0           0
Fetch      100    212.87     207.84          0    1093000          0         100
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total      201    212.87     207.85          0    1093000          0         100

SELECT count(*) from (
       select * from (
       select row_number() over(order by object_id,rn) countnum,t.* from sort_test t)
       where countnum>0 and countnum<=50
    )

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute    100      0.01       0.00          0          0          0           0
Fetch      100    169.29     165.32          0    1093000          0         100
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total      201    169.30     165.33          0    1093000          0         100