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Thread: Set Membership SQL

  1. #1
    Mark Marlow Guest

    Set Membership SQL

    Given a table T, with 2 columns Item and RequiredParts.

    Where Item is the name of an item and RequiredParts is the name of
    a part that an Item depends on.

    Example table T:
    Item , RequiredParts
    A , 1
    A , 2
    B , 1
    B , 3
    C , 1
    C , 2
    C , 3
    D , 1
    D , 2

    So
    A depends on 1 & 2
    B depends on 1 & 3
    C depends on 1, 2 & 3
    D depends on 1 & 2

    Can a query be written such that the input is
    the available Required parts, and the result
    is the list of items that have dependencies
    fullfilled.

    Ex. f(1) = null
    f(1,2) = A,D
    f(1,2,3) = C
    f(1,3) = B



  2. #2
    Mark Marlow Guest

    Set Membership SQL - Answer

    Answer:

    SELECT DISTINCT Item FROM T WHERE ITEM NOT IN(SELECT ITEM FROM T WHERE RequiredParts NOT IN(1,2,3))



    ------------
    Mark Marlow at 8/19/99 9:07:44 AM

    Given a table T, with 2 columns Item and RequiredParts.

    Where Item is the name of an item and RequiredParts is the name of
    a part that an Item depends on.

    Example table T:
    Item , RequiredParts
    A , 1
    A , 2
    B , 1
    B , 3
    C , 1
    C , 2
    C , 3
    D , 1
    D , 2

    So
    A depends on 1 & 2
    B depends on 1 & 3
    C depends on 1, 2 & 3
    D depends on 1 & 2

    Can a query be written such that the input is
    the available Required parts, and the result
    is the list of items that have dependencies
    fullfilled.

    Ex. f(1) = null
    f(1,2) = A,D
    f(1,2,3) = C
    f(1,3) = B



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