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use of GROUP BY in SELECT

I am considering using GROUP BY in several selects where I will access very big bsik, bsid, bsad, bsak, ecc...

My two concerns are performance and high data volume.

GROUP BY should reduce data arriving from DB but will it hurt performance?

What are your considerations?

Any ideas are welcome. I cannot seem to find anything specific for or against GROUP BY.

thanks,

Phillip

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    author's profile photo Former Member
    Former Member
    Posted on Feb 02, 2005 at 09:48 AM

    Hello Philip,

    I would advise that you do not use the Group By clause in the select statements for these tables. As you have rightly said, the data volume in these tables might be a major cause for concern.

    Using the Group By clause will heavily load the database server. while in the development environment, your query might run okay, in the productive environment it might crash. The reason : the cursor to the database would have timed out.

    The Group By operation, as you know can be simulated after you get the data into the application server. The application server processing can take some time but you can usually optimize it.

    Regards,

    Anand Mandalika.

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  • Posted on Feb 02, 2005 at 12:59 PM

    Hi Phillip,

    good to hear you go for an other way.

    IMHO GROUP BY makes sense only with aggregations (like COUNT( * ), MAX( LFDNR ),...). Then grouping will bring you a bunch of counts, which would otherwise have to be selected step by step.

    That's hard work for database, but faster then getting all entries and looping + counting on application server (in general, depends of course on factor (total number of entries) / (number of groups) ).

    In your situation, you most likely need all entries anyway.

    Regards,

    Christian

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