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Optimization of nested queries

Posted on 2008-10-23
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Last Modified: 2013-12-18
Is there a more optimized way to wirte the below query, if yes how and why !

select e.DSORGUT as AGENCEDSORGUT, e.CDORGFNC as AGENCECDORGFNC, e.NOBRN as AGENCENOBRN,
            f.DSORGUT as AGENCEDSORGUT, f.CDORGFNC as AGENCECDORGFNC, f.NOBRN as AGENCENOBRN,
            g.DSORGUT as AGENCEDSORGUT, g.CDORGFNC as AGENCECDORGFNC, g.NOBRN as AGENCENOBRN
       from SYNOUP e, SYNOUP f, SYNOUP g
       where e.NOINP = (select b.NOINPREL from SYNRIP b, SYNREF c where b.NOINP = c.NOINP and b.CDRIC = 'A' and b.CDRIC IS NOT NULL )
       and f.NOINP = (select b.NOINPREL from SYNRIP b, SYNREF c where b.NOINP = c.NOINP and b.CDRIC = 'D' and b.CDRIC IS NOT NULL )
       and g.NOINP = (select b.NOINPREL from SYNRIP b, SYNREF c where b.NOINP = c.NOINP and b.CDRIC = 'R' and b.CDRIC IS NOT NULL )
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Question by:gursheenz2008
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Expert Comment

by:GGuzdziol
ID: 22784988

with adr as (
  select 
      max(case when b.CDRIC = 'A' THEN b.NOINPREL else null end) as noinprel_a, 
      max(case when b.CDRIC = 'D' THEN b.NOINPREL else null end) as noinprel_d, 
      max(case when b.CDRIC = 'R' THEN b.NOINPREL else null end) as noinprel_r, 
    from SYNRIP b, SYNREF c 
    where b.NOINP = c.NOINP and b.CDRIC in ('A', 'D', 'R') and b.CDRIC IS NOT NULL
)
select e.DSORGUT as AGENCEDSORGUT, e.CDORGFNC as AGENCECDORGFNC, e.NOBRN as AGENCENOBRN,
            f.DSORGUT as AGENCEDSORGUT, f.CDORGFNC as AGENCECDORGFNC, f.NOBRN as AGENCENOBRN,
            g.DSORGUT as AGENCEDSORGUT, g.CDORGFNC as AGENCECDORGFNC, g.NOBRN as AGENCENOBRN
       from SYNOUP e, SYNOUP f, SYNOUP g, adr
     where e.NOINP = adr.noinprel_a
       and f.NOINP = adr.noinprel_d
       and g.NOINP = adr.noinprel_r

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Expert Comment

by:GGuzdziol
ID: 22784994
This techinique is called "Subquery factoring".
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Author Comment

by:gursheenz2008
ID: 22785432
Thanks for this !

Please correct my understanding !

1.max(case when b.CDRIC = 'A' THEN b.NOINPREL else null end) as noinprel_a,
 This will take the MAX of NOINPREL if there's a value, else null value.

Why we again need b.CDRIC in ('A', 'D', 'R')?

2. "with"  Clause will treat the result of the query as a temp table(GTT)/ in line view.

3. This is not a PL/SQL block, it's a SQL statement

with adr as ( ... ) select ...
       and g.NOINP = adr.noinprel_r ;

4.When Oracel will drop this temp table(GTT)/ in line view.
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Expert Comment

by:sdstuber
ID: 22785445
is noinp a unique key for synoup?
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Accepted Solution

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GGuzdziol earned 1000 total points
ID: 22785535
1. It may make Oracle uses index on that field.
2&4. Results of the query will be put in temporary table in temporary tablespace. Once query is finished space may be reused by other processes.
3. Yes, it's SQL statement: http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_10002.htm#i2077142
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