विश्लेषणात्मक फ़ंक्शन प्रदर्शन अनुक्रमणिका स्तंभ क्रम पर निर्भर हो सकता है। इंडेक्स को (ACCTNUM,DEPT_NUM) . से बदलना करने के लिए (DEPT_NUM,ACCTNUM) लागत कम कर सकता है और अस्थायी टेबलस्पेस की आवश्यकता को दूर कर सकता है।
partition by COL_2 order by COL_1 => INDEX FAST FULL SCAN|WINDOW SORT PUSHED RANK
partition by COL_1 order by COL_2 => INDEX FULL SCAN|WINDOW NOSORT
INDEX FAST FULL SCAN तेज़ मल्टी-ब्लॉक IO का उपयोग करता है, लेकिन इसके लिए डेटा को सॉर्ट करना और सॉर्ट क्षेत्र के लिए संभवतः अस्थायी टेबलस्पेस की भी आवश्यकता होती है।
INDEX FULL SCAN धीमे सिंगल-ब्लॉक IO का उपयोग करता है लेकिन यह डेटा को क्रम में लौटाता है और सॉर्टिंग से बचता है।
नमूना स्कीमा और डेटा
--drop table mytable;
create table mytable(dept_num number not null, acctnum number not null
,a number, b number, c number, d number, e number);
insert into mytable
select 1 dept_num, 1 acctnum, 0,0,0,0,0 from dual union all
select 1 dept_num, 2 acctnum, 0,0,0,0,0 from dual union all
select 1 dept_num, 3 acctnum, 0,0,0,0,0 from dual union all
select 2 dept_num, 1 acctnum, 0,0,0,0,0 from dual union all
select 2 dept_num, 2 acctnum, 0,0,0,0,0 from dual union all
select 3 dept_num, 1 acctnum, 0,0,0,0,0 from dual;
--Create 600K similar rows.
insert into mytable
select dept_num + rownumber*3, acctnum, a,b,c,d,e
from mytable
cross join (select level rownumber from dual connect by level <= 100000);
begin
dbms_stats.gather_table_stats(user, 'mytable');
end;
/
(ACCTNUM,DEPT_NUM) =विंडो सॉर्ट पुश रैंक
create index mytable_idx on mytable(acctnum, dept_num);
explain plan for
select dept_num, acctnum from
(
select dept_num, acctnum
,row_number() over (partition by dept_num order by acctnum) as row_identifier
from mytable
)
where row_identifier between 1 and 10;
select * from table(dbms_xplan.display);
Plan hash value: 952182109
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 600K| 22M| | 1625 (3)| 00:00:23 |
|* 1 | VIEW | | 600K| 22M| | 1625 (3)| 00:00:23 |
|* 2 | WINDOW SORT PUSHED RANK| | 600K| 4687K| 9424K| 1625 (3)| 00:00:23 |
| 3 | INDEX FAST FULL SCAN | MYTABLE_IDX | 600K| 4687K| | 239 (3)| 00:00:04 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("ROW_IDENTIFIER">=1 AND "ROW_IDENTIFIER"<=10)
2 - filter(ROW_NUMBER() OVER ( PARTITION BY "DEPT_NUM" ORDER BY "ACCTNUM")<=10)
(DEPT_NUM,ACCTNUM) =विंडो NOSORT
drop index mytable_idx;
create index mytable_idx on mytable(dept_num, acctnum);
explain plan for
select dept_num, acctnum from
(
select dept_num, acctnum
,row_number() over (partition by dept_num order by acctnum) as row_identifier
from mytable
)
where row_identifier between 1 and 10;
select * from table(dbms_xplan.display);
Plan hash value: 1773829932
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 600K| 22M| 792 (2)| 00:00:12 |
|* 1 | VIEW | | 600K| 22M| 792 (2)| 00:00:12 |
|* 2 | WINDOW NOSORT | | 600K| 4687K| 792 (2)| 00:00:12 |
| 3 | INDEX FULL SCAN| MYTABLE_IDX | 600K| 4687K| 792 (2)| 00:00:12 |
---------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("ROW_IDENTIFIER">=1 AND "ROW_IDENTIFIER"<=10)
2 - filter(ROW_NUMBER() OVER ( PARTITION BY "DEPT_NUM" ORDER BY
"ACCTNUM")<=10)
