Is there a way I can reduce the impact of the 'ORDER BY lro_pid' clause in the OVER portion of the inner query below?
SELECT *
FROM (SELECT a.*,
Row_Number() over (PARTITION BY search_point_type
ORDER BY lro_pid) spt_rank
FROM lro_search_point a
ORDER BY spt_rank)
WHERE spt_rank = 1;
I don't care to order this result within the partition since I want to order it by a different variable entirely. lro_pid is an indexed column, but this still seems like a waste of resources as it currently stands. (Perhaps there is a way to limit the ordering to a range of a single row?? Hopefully no time/energy would be spent on sorting within the partition at all)
A couple of things to try:
Can you e.g. ORDER BY 'constant'
in the OVER clause?
If ordering by a constant is not permitted, how about ORDER BY (lro_pid * 0)
?
I'm not an Oracle expert (MSSQL is more my thing) - hence questions to answer your question!
Using a constant in the analytic ORDER BY as @Will A suggested appears to be the fastest method. The optimizer still performs a sort, but it's faster than sorting a column. Also, you probably want to remove the second ORDER BY, or at least move it to the outer query.
Below is my test case:
--Create table, index, and dummy data.
create table lro_search_point(search_point_type number, lro_pid number, column1 number
,column2 number, column3 number);
create index lro_search_point_idx on lro_search_point(lro_pid);
insert /*+ append */ into lro_search_point
select mod(level, 10), level, level, level, level from dual connect by level <= 100000;
commit;
--Original version. Averages 0.53 seconds.
SELECT * FROM
(
SELECT a.*, Row_Number() over (PARTITION BY search_point_type ORDER BY lro_pid) spt_rank
FROM lro_search_point a
ORDER BY spt_rank
)
WHERE spt_rank=1;
--Sort by constant. Averages 0.33 seconds.
--This query and the one above have the same explain plan, basically it's
--SELECT/VIEW/SORT ORDER BY/WINDOW SORT PUSHED RANK/TABLE ACCESS FULL.
SELECT * FROM
(
SELECT a.*, Row_Number() over (PARTITION BY search_point_type ORDER BY -1) spt_rank
FROM lro_search_point a
ORDER BY spt_rank
)
WHERE spt_rank=1;
--Remove the ORDER BY (or at least move it to the outer query). Averages 0.27 seconds.
SELECT * FROM
(
SELECT a.*, Row_Number() over (PARTITION BY search_point_type ORDER BY -1) spt_rank
FROM lro_search_point a
)
WHERE spt_rank=1;
--Replace analytic with aggregate functions, averages 0.28 seconds.
--This idea is the whole reason I did this, but turns out it's no faster. *sigh*
--Plan is SELECT/SORT GROUP BY/TABLE ACCESS FULL.
--Note I'm using KEEP instead of just regular MIN.
--I assume that you want the values from the same row.
SELECT a.search_point_type
,min(lro_pid) keep (dense_rank first order by -1)
,min(column1) keep (dense_rank first order by -1)
,min(column2) keep (dense_rank first order by -1)
,min(column3) keep (dense_rank first order by -1)
FROM lro_search_point a
group by a.search_point_type;
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