分页SQL取下一页

20条记录一页,扫描第2页就需要访问40条记录。

SQL> select * from ( select * from ( select /*+ index_desc(a idx_page_3) */ a.*,rownum rn   from page
a  where object_id >1000 and owner='SYS'  order by object_id desc ) where rownum<=40 ) where
rn>=21  2    3
  4  ;

SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------
SQL_ID	bwcbf54a6h4th, child number 1
-------------------------------------
select * from ( select * from ( select /*+ index_desc(a idx_page_3) */
a.*,rownum rn	from page a  where object_id >1000 and owner='SYS'
order by object_id desc ) where rownum<=40 ) where rn>=21

Plan hash value: 3526010999

---------------------------------------------------------------------------------------------------------
| Id  | Operation			 | Name       | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
---------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT		 |	      |      1 |	|     20 |00:00:00.01 |      10 |
|*  1 |  VIEW				 |	      |      1 |     40 |     20 |00:00:00.01 |      10 |
|*  2 |   COUNT STOPKEY 		 |	      |      1 |	|     40 |00:00:00.01 |      10 |
|   3 |    VIEW 			 |	      |      1 |  30556 |     40 |00:00:00.01 |      10 |
|   4 |     COUNT			 |	      |      1 |	|     40 |00:00:00.01 |      10 |
|   5 |      TABLE ACCESS BY INDEX ROWID | PAGE       |      1 |  30556 |     40 |00:00:00.01 |      10 |
|*  6 |       INDEX RANGE SCAN DESCENDING| IDX_PAGE_3 |      1 |  30556 |     40 |00:00:00.01 |       4 |
---------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("RN">=21)
   2 - filter(ROWNUM<=40)
   6 - access("OBJECT_ID" IS NOT NULL AND "OBJECT_ID">1000 AND "OWNER"='SYS')
       filter("OWNER"='SYS')

28 rows selected.

SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------
SQL_ID	6gay6kkxxsqgw, child number 0
-------------------------------------
select * from ( select * from ( select /*+ index_desc(a idx_page_3) */
a.*,rownum rn	from page a  where object_id >1000 and owner='SYS'
order by object_id desc ) where rownum<=60 ) where rn>=41

Plan hash value: 3526010999

---------------------------------------------------------------------------------------------------------
| Id  | Operation			 | Name       | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
---------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT		 |	      |      1 |	|     20 |00:00:00.01 |      11 |
|*  1 |  VIEW				 |	      |      1 |     60 |     20 |00:00:00.01 |      11 |
|*  2 |   COUNT STOPKEY 		 |	      |      1 |	|     60 |00:00:00.01 |      11 |
|   3 |    VIEW 			 |	      |      1 |  30556 |     60 |00:00:00.01 |      11 |
|   4 |     COUNT			 |	      |      1 |	|     60 |00:00:00.01 |      11 |
|   5 |      TABLE ACCESS BY INDEX ROWID | PAGE       |      1 |  30556 |     60 |00:00:00.01 |      11 |
|*  6 |       INDEX RANGE SCAN DESCENDING| IDX_PAGE_3 |      1 |  30556 |     60 |00:00:00.01 |       4 |
---------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("RN">=41)
   2 - filter(ROWNUM<=60)
   6 - access("OBJECT_ID" IS NOT NULL AND "OBJECT_ID">1000 AND "OWNER"='SYS')
       filter("OWNER"='SYS')

28 rows selected.