分页语句模板

分页语句方法:

1.rownum 
2.row_number over(order by column) as 行号

例子:
create table page as select * from dba_objects;

create index idx_page_1 on page(object_id,owner);
BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'QUERY',
                                tabname          => 'PAGE',
                                estimate_percent => 100,
                                method_opt       => 'for all columns size skewonly',
                                no_invalidate    => FALSE,
                                degree           => 4,
                                cascade          => TRUE);
END;
/

比如这个SQL

select object_id from 
(
select * from 
(
select  a.*,rownum rn
  from page a 
 where object_id >1000 and owner='SYS'
 order by object_id 
) where rownum<=20
) where rn>=0;

SQL> select min(object_id) ,max(object_id) from page where owner='SYS' and object_id>1000;

MIN(OBJECT_ID) MAX(OBJECT_ID)
-------------- --------------
	  1001	       111148


SQL> set linesize 200
SQL> set pagesize 200
SQL> alter session set statistics_level=all; 

会话已更改。

SQL> select object_id from 
(
select * from 
(
select  a.*,rownum rn
  from page a 
 where object_id >1000 and owner='SYS'
 order by object_id 
) where rownum<=20
) where rn>=0;  2    3    4    5    6    7    8    9   10  

 OBJECT_ID
----------
      1001
      1002
      1003
      1004
      1005
      1006
      1007
      1008
      1009
      1010
      1011
      1012
      1013
      1014
      1015
      1016
      1017
      1018
      1019
      1020

已选择20行。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	dfb5uh3bgs11m, child number 0
-------------------------------------
select object_id from ( select * from ( select	a.*,rownum rn	from
page a	where object_id >1000 and owner='SYS'  order by object_id )
where rownum<=20 ) where rn>=0

Plan hash value: 2584750597

---------------------------------------------------------------------------------------------
| Id  | Operation	     | Name	  | Starts | E-Rows | A-Rows |	 A-Time   | Buffers |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |		  |	 1 |	    |	  20 |00:00:00.01 |	  4 |
|*  1 |  VIEW		     |		  |	 1 |	 20 |	  20 |00:00:00.01 |	  4 |
|*  2 |   COUNT STOPKEY      |		  |	 1 |	    |	  20 |00:00:00.01 |	  4 |
|   3 |    VIEW 	     |		  |	 1 |  37466 |	  20 |00:00:00.01 |	  4 |
|   4 |     COUNT	     |		  |	 1 |	    |	  20 |00:00:00.01 |	  4 |
|*  5 |      INDEX RANGE SCAN| IDX_PAGE_1 |	 1 |  37466 |	  20 |00:00:00.01 |	  4 |
---------------------------------------------------------------------------------------------

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

   1 - filter("RN">=0)
   2 - filter(ROWNUM<=20)
   5 - access("OBJECT_ID">1000 AND "OWNER"='SYS' AND "OBJECT_ID" IS NOT NULL)
       filter("OWNER"='SYS')


已选择27行。


ORACLE升序扫描了索引，扫描20条记录就停止了.


继续取下一页,
SQL> select object_id from 
(
select * from 
(
select  a.*,rownum rn
  from page a 
 where object_id >1000 and owner='SYS'
 order by object_id 
) where rownum<=40
) where rn>=21;  2    3    4    5    6    7    8    9   10  

 OBJECT_ID
----------
      1021
      1022
      1023
      1024
      1025
      1026
      1027
      1028
      1029
      1030
      1031
      1032
      1033
      1034
      1035
      1036
      1037
      1038
      1039
      1040

已选择20行。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	ftvyz3pxdfvyf, child number 0
-------------------------------------
select object_id from ( select * from ( select	a.*,rownum rn	from
page a	where object_id >1000 and owner='SYS'  order by object_id )
where rownum<=40 ) where rn>=21

Plan hash value: 2584750597

---------------------------------------------------------------------------------------------
| Id  | Operation	     | Name	  | Starts | E-Rows | A-Rows |	 A-Time   | Buffers |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |		  |	 1 |	    |	  20 |00:00:00.01 |	  4 |
|*  1 |  VIEW		     |		  |	 1 |	 40 |	  20 |00:00:00.01 |	  4 |
|*  2 |   COUNT STOPKEY      |		  |	 1 |	    |	  40 |00:00:00.01 |	  4 |
|   3 |    VIEW 	     |		  |	 1 |  37466 |	  40 |00:00:00.01 |	  4 |
|   4 |     COUNT	     |		  |	 1 |	    |	  40 |00:00:00.01 |	  4 |
|*  5 |      INDEX RANGE SCAN| IDX_PAGE_1 |	 1 |  37466 |	  40 |00:00:00.01 |	  4 |
---------------------------------------------------------------------------------------------

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

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


已选择27行。

可以看到取下一页20行时,需要访问40条记录


继续取下一页
SQL> select object_id from 
(
select * from 
(
select  a.*,rownum rn
  from page a 
 where object_id >1000 and owner='SYS'
 order by object_id 
) where rownum<=60
) where rn>=41;  2    3    4    5    6    7    8    9   10  

 OBJECT_ID
----------
      1041
      1042
      1043
      1044
      1045
      1046
      1047
      1048
      1049
      1050
      1051
      1052
      1053
      1054
      1055
      1056
      1057
      1058
      1059
      1060

已选择20行。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	9xj40t5wq2n8v, child number 0
-------------------------------------
select object_id from ( select * from ( select	a.*,rownum rn	from
page a	where object_id >1000 and owner='SYS'  order by object_id )
where rownum<=60 ) where rn>=41

Plan hash value: 2584750597

---------------------------------------------------------------------------------------------
| Id  | Operation	     | Name	  | Starts | E-Rows | A-Rows |	 A-Time   | Buffers |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |		  |	 1 |	    |	  20 |00:00:00.01 |	  4 |
|*  1 |  VIEW		     |		  |	 1 |	 60 |	  20 |00:00:00.01 |	  4 |
|*  2 |   COUNT STOPKEY      |		  |	 1 |	    |	  60 |00:00:00.01 |	  4 |
|   3 |    VIEW 	     |		  |	 1 |  37466 |	  60 |00:00:00.01 |	  4 |
|   4 |     COUNT	     |		  |	 1 |	    |	  60 |00:00:00.01 |	  4 |
|*  5 |      INDEX RANGE SCAN| IDX_PAGE_1 |	 1 |  37466 |	  60 |00:00:00.01 |	  4 |
---------------------------------------------------------------------------------------------

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

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


已选择27行。

取第三页时需要访问60条记录


下面进行降序排序:


SQL> select object_id from 
(
select * from 
(
select  a.*,rownum rn
  from page a 
 where object_id >1000 and owner='SYS'
 order by object_id desc
) where rownum<=20
) where rn>=0;  2    3    4    5    6    7    8    9   10  

 OBJECT_ID
----------
    111148
    111147
    111146
    111122
    111121
    111098
    111097
    111075
    111074
    111050
    111049
    111025
    111024
    111000
    110999
    110975
    110974
    110950
    110949
    110924

已选择20行。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	fbp9fbq0suc6c, child number 0
-------------------------------------
select object_id from ( select * from ( select	a.*,rownum rn	from
page a	where object_id >1000 and owner='SYS'  order by object_id desc
) where rownum<=20 ) where rn>=0

Plan hash value: 512348098

--------------------------------------------------------------------------------------------------------
| Id  | Operation			| Name	     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT		|	     |	    1 |        |     20 |00:00:00.01 |	     4 |
|*  1 |  VIEW				|	     |	    1 |     20 |     20 |00:00:00.01 |	     4 |
|*  2 |   COUNT STOPKEY 		|	     |	    1 |        |     20 |00:00:00.01 |	     4 |
|   3 |    VIEW 			|	     |	    1 |  37466 |     20 |00:00:00.01 |	     4 |
|   4 |     COUNT			|	     |	    1 |        |     20 |00:00:00.01 |	     4 |
|*  5 |      INDEX RANGE SCAN DESCENDING| IDX_PAGE_1 |	    1 |  37466 |     20 |00:00:00.01 |	     4 |
--------------------------------------------------------------------------------------------------------

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

   1 - filter("RN">=0)
   2 - filter(ROWNUM<=20)
   5 - access("OBJECT_ID" IS NOT NULL AND "OBJECT_ID">1000 AND "OWNER"='SYS')
       filter("OWNER"='SYS')


已选择27行。

ORACLE降序扫描了索引，扫描20条记录就停止了.

继续降序取下一页:



SQL> select object_id from 
(
select * from 
(
select  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    5    6    7    8    9   10  
 OBJECT_ID
----------
    109638
    109637
    105456
    105455
    104527
    104526
    104415
     94031
     87442
     87441
     87440
     87439
     87438
     87437
     87436
     87435
     87434
     87433
     87432
     87431

已选择20行。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	09ryhg66tgad5, child number 0
-------------------------------------
select object_id from ( select * from ( select	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: 512348098

--------------------------------------------------------------------------------------------------------
| Id  | Operation			| Name	     | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT		|	     |	    1 |        |     20 |00:00:00.01 |	    31 |
|*  1 |  VIEW				|	     |	    1 |     40 |     20 |00:00:00.01 |	    31 |
|*  2 |   COUNT STOPKEY 		|	     |	    1 |        |     40 |00:00:00.01 |	    31 |
|   3 |    VIEW 			|	     |	    1 |  37466 |     40 |00:00:00.01 |	    31 |
|   4 |     COUNT			|	     |	    1 |        |     40 |00:00:00.01 |	    31 |
|*  5 |      INDEX RANGE SCAN DESCENDING| IDX_PAGE_1 |	    1 |  37466 |     40 |00:00:00.01 |	    31 |
--------------------------------------------------------------------------------------------------------

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

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


已选择27行。


这个时候降序分页取下一页需要访问40条记录。


总结:
1.分页语句必须走索引,在分页语句的WHERE 条件列和order by列上创建组合索引

2.分页语句两边快,越到中间越慢,因为索引要访问的记录更多