Oracle-L: Re: Select Statement Gone South??

From: Mark Richard <mrichard_at_transurban.com.au>
Date: Tue, 25 Feb 2003 18:48:53 -0800
Message-ID: <F001.0055978E.20030225184853@fatcity.com>

Laura,

Unfortunately it's hard to provide advice without knowing a lot more about the tables, the cardinality of the columns in the where clause, and perhaps even whether there are tricks we might be able to abuse by knowing information about the data that's not immediately obvious.

Ignoring that, an explain plan (as requested by Connor) will certainly help. Other things that would help are row counts of each table, and for the columns in the where clause what is there selectivity like.

One way to determine selectivity would be something like:

select count(*) total_rows,

     sum(decode(pre_approved_purch_flag, 'N', 1, 0)) pre_app_is_n,
     sum(decode(company_reimburse_flag, 'Y', 1, 0)) com_reim_is_y,
     sum(decode(pre_approved_purch_flag||company_reimburse_flag, 'NY', 1,

0)) both_cond_met
from part_master_catalogs

This will give an idea of how many rows meet each criteria, and how many meet both criteria. This may then give some hint as to whether an index access path is worthwhile or whether a full table scan is quicker. Is there a magic figure to determine which is faster? No. But the extremes (like 1% and 90%) will be obvious.

With regard to your specific query, I would ensure that the subselect performs very fast since it is probably being called in some kind of nested loop. Since some of the columns in the subselect aren't prefixed with a table alias I can't even work out which table they necessarily come from.

Regards,

Mark.

                                                                                                                   
                    "Burton, Laura                                                                                 
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                    plus.com>            Subject:     Select Statement Gone South??                                
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                    26/02/2003                                                                                     
                    12:23                                                                                          
                    Please respond                                                                                 
                    to ORACLE-L

I am inserting records into a table based on a select statement and it is taking way too much time. I have created indexes of the foreign keys and tried to rearrange the where clause to omit records earlier, but to no avail. The statement looks like this:

Insert into table test

select part_num,

nomenclature,

to_char(requisition_date,'yddd') ||lpad(preq.document_serial,4,0),

2, /* '53-Purchase' */

PSA.TRANS_date,

requisition_qty,

unit_price,

4 /* 'ALMD Disapproval' */

from part_master_catalogs pmc,

part_requisitions preq,

part_price_histories pph,

part_status_assocs psa

where preq.pmc_id_fk = pmc.pmc_id

and preq.preq_id = psa.preq_id_fk

and psa.req_status_cd_fk = 'D'

AND PSA.TRANS_DATE <= TO_DATE('&&NEWMEDATE','MM-DD-YYYY')

AND PSA.TRANS_DATE > TO_DATE('&&LASTMEDATE','MM-DD-YYYY') and pmc.pre_approved_purch_flag = 'N'

and pmc.company_reimburse_flag = 'Y'

and pph.pph_id = (select max(pph_id) from part_price_histories

                            where preq.pmc_id_fk = pmc_id_fk


                              and requisition_date >= effective_date)

Any ideas?? Any insight would be appreciated.

Thanks,

Laura

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Author: Mark Richard
  INET: mrichard_at_transurban.com.au

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Received on Tue Feb 25 2003 - 20:48:53 CST