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  1. #1
    Join Date
    Mar 2003

    Relational Algebra Trees

    Relational algebra Trees, i have converted my sql to relational algebra. does anyone know how to make it into a tree?
    Tryin to understand these things, does anyone know anything about them?

    UNION Table1 AND Table2 OVER code giving T1
    RESTRICT T1 where code = NULL giving T2
    PROJECT T2 OVER Table1


  2. #2
    Join Date
    May 2002
    Florida, USA
    Hmm... I have been playing with relational algebra, while reading C.J. Date's Introduction to Database Systems and Foundation for Future Database Systems. At the moment I don't remember how trees are implemented in a truly relational language, but apparently they are much better implemented in relational algebra than in the typical SQL "CONNECT BY".

    You might try either of those books, or see if you can find some info on Fabian Pascal's Database Debunkings

    See this discussion from Pascal's site:

    When I have the time, I might look that syntax up and get back to you .

    (One note: the "pure" relational algebra people say NULLs are a bad idea. And, in true formal logic, a NULL is unknown, thus you can't test it for equality with anything; you can only test if something IS or IS NOT NULL)

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