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  1. #1
    Join Date
    Aug 2003
    Location
    Boise, ID
    Posts
    2

    Question Unanswered: Access Query mechanics and improving performance

    Hello,

    Can anyone out here explain how a query works? I've been working off of a half-remembered explanation from way back when and would like a better understanding (so I can optimize performance).

    What I recall is this... With two or more tables, SQL generates Cartesian output (initial results come from multiplication). The multiplied output is then limited based on the joins/criteria supplied.

    I'm hoping that someone can expand on this or recommend a resource which will explain the process behind a query and how the process is affected by joins & indices.

    Thanks,
    Steve

  2. #2
    Join Date
    Aug 2003
    Location
    Bosnia & Hercegovina
    Posts
    57
    maybe you should take a book on SQL, like Teach Yourself SQL In 21 Days....

    SQL is 4GL (generation language) and is nonprocedural, meaning that it is not about how to get result, but about what result to get.....

    in that sense it doesn't matter what happens first and what last when query is executed, unless you are writting query engine......

    all table relations and joins affect result set by including or excluding some elements of original sets....

    attached is a sample chapter from the book I mentioned.....

    book is about SQL in general, not about access queries.......
    Attached Files Attached Files

  3. #3
    Join Date
    Aug 2003
    Location
    Boise, ID
    Posts
    2
    Strucnjak, thanks for the info/recommendation!

    I've browsed a little for books and haven't hit on specifically what I'm looking for... What I'm trying to do is put together information for a "class" at work. Our Access development has come about largely by trial and error. What we've seen are databases that aren't normalized enough, and databases which have taken normalization too far (i.e. respone time/performance suffers). I'm interested in an explanation for how SQL compiles results as a means of illustrating where normalization adds value and where it doesn't.

    Thanks,
    Steve

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