oracle: better the perfomrnace. inner join vs partition by

Posted on 2011-03-02
Last Modified: 2013-12-07
I have 2 querys, the former takes more than 15 minutes.
query 1
from        tmp_Solicitud ts1 inner join tmp_Solicitud ts2
            on ts1.CODSOLICITUD = ts2.CODSOLICITUD
            and ts2.codsolicitud = (select max(t.codsolicitud)
                                    from tmp_Solicitud t  
                                    where ts2.CodUnico = t.CodUnico);  

query 2
  FROM (SELECT codunico,
               CASE codtipobanca
                   WHEN 1 THEN 'Corporativa BC'
                   WHEN 2 THEN 'Empresa BE'
                   WHEN 3 THEN 'Institucional BI'
                   WHEN 4 THEN 'Leasing LS'
               CASE codsegmentacion WHEN '1' THEN '1' ELSE '0' END codsegmentacion,
               RANK() OVER (PARTITION BY codunico ORDER BY codsolicitud DESC) r
          FROM tmp_solicitud)
 WHERE r = 1

Thanks to you, the query was modified and now takes less than 2 seconds, my question is why?
 Deputy respective execution plans.

Question by:enrique_aeo
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LVL 73

Assisted Solution

sdstuber earned 500 total points
ID: 35021499
The first queries the same table 3 times including extra work for aggregation and filtering on the aggregate

The second queries the table only once and then sorts the data.

The first does a lot more work, hence more time
LVL 73

Accepted Solution

sdstuber earned 500 total points
ID: 35021540

select .... from (select....)

might make it appear there are two queries needing double io, but there isn't.  The inner query is called an inline view and is merely a logical construction for syntax.  Looking at the plan you can see there is only one IO  (TABLE ACCESS FULL) which makes sense since the table is only referenced once in the query (the FROM clause)

the other query clearly  references the table 3 times, so regardless of any syntax constructions the query will hit the table 3 times once for each reference and the plan shows that
LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
ID: 35021570
Since your question has to do with performance:  What version of Oracle are you using?

I noticed you are using Rule-Based Optimization.  If possible and you aren't using it 'by choice', I would look into using Cost-Based Optimization.

Check the online documentation for your version.

Here's the 11Gr2 link (It's what I have bookmarked):
LVL 73

Assisted Solution

sdstuber earned 500 total points
ID: 35021606
I agree switching to CBO from RBO is a good idea,
 but it's not actually related to the specific reason why query 2 is better than query 1.

Since you're able to use the RANK analytic that means you're using at least 8.1  so CBO is definitely an option to investigate.
LVL 76

Expert Comment

by:slightwv (䄆 Netminder)
ID: 35021656
>>but it's not actually related to the specific reason why query 2 is better than query 1.

As they are currently written, I agree and should have commented on that.

please do not award any points to my post on RBO versus CBO.


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