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From: "Thomas T(dot) Veldhouse" <veldy(at)veldy(dot)net>
To: "tamsin" <tg_mail(at)bryncadfan(dot)co(dot)uk>, "PostgreSQL-general" <pgsql-general(at)postgreSQL(dot)org>
Subject: Re:
Date: 2001-06-29 16:31:22
Message-ID: 009d01c100b8$ef4b8190$ (view raw, whole thread or download thread mbox)
Lists: pgsql-generalpgsql-sql
Heck, you could refine it this way as well.

select pm.*
from purchasemaster pm
  inner join itemmaster im
    on (pm.transactionid = im.transactionid and im.itempriority = 2)

This might reduce memory usage.  I am not sure which will turn out to perform better in a resource friendly environment.

Tom Veldhouse

PS  There is a lot of HTML email on this list.  Is this generally considered good?  Or should I convert my replies to text?

----- Original Message ----- 
  From: Thomas T. Veldhouse 
  To: tamsin ; PostgreSQL-general 
  Sent: Friday, June 29, 2001 10:58 AM
  Subject: Re: [GENERAL] 

  select pm.*
  from purchasemaster pm
    inner join itemmaster im
      on pm.transactionid = im.transactionid
  where im.itempriority = 2

  Try this instead.

  Make sure the appropriate indexes (on pm.transactionid, im.transactionid and im.itempriority) exist if the tables are of any appreciable size.  

  Tom Veldhouse

    ----- Original Message ----- 
    From: tamsin 
    To: pgsql-general(at)postgresql(dot)org 
    Sent: Friday, June 29, 2001 7:40 AM
    Subject: RE: [GENERAL] 

    i think performance is better in postgres if you rewrite this sort of query as:

    select * from purchasemaster where exists (select 1 from itemmaster where itempriority = 2 and transactionid = purchasemaster.transactionid)

    hope this helps,

      -----Original Message-----
      From: pgsql-general-owner(at)postgresql(dot)org [mailto:pgsql-general-owner(at)postgresql(dot)org]On Behalf Of Kapil Tilwani
      Sent: 28 May 2001 12:27
      To: pgsql-general(at)postgresql(dot)org; pgsql-sql(at)postgresql(dot)org
      Subject: [GENERAL] 


      I have two tables purchasemaster (Master) and ItemMaster (child) linked through TransactionID

      I have a query like
      select * from purchasemaster where transactionid in (select transactionid from itemmaster where itempriority = 2)

      ****I need this query for MS-Access, MS-SQL and Postgres.  Because the application is supposed to be such that for upto 2-3 users, the application would be running on MS-Access or MSDE, while for heavier databases i.e., greater than 4 , the ideal database would be Postgres

      Only the problem is ...  (correct me if i am wrong, PLEEEEEEEEEEEASE) that for each tuple in purchasemaster the sub-query is re-evaluated (True or False????).  What I am looking at is whether it is possible to execute the query in the sub-query just once, get its value as in "(1,2,5,23,7,90)", etc. in place of the sub-query and accordingly, execute the main query.

      Thank you,

In response to

  • Re: at 2001-06-29 15:58:11 from Thomas T. Veldhouse


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