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Other Operations

  1. Some other equivalences for union and set difference:





  2. Our text covers only some of the possible operations. (For a more complete list, see Elmasri & Navathe, page 518.)

    Also, it makes sense to combine the implementation of various sets of operations in order to reduce the size of intermediate relations:

    • Combine projects and selects with a Cartesian product or natural join.
    • The idea is to do the selection and/or projection while computing the join.
    • This saves computing a large intermediate relation that is going to be subsequently reduced by the select or project anyway.

Osmar Zaiane
Sun Jul 26 17:45:14 PDT 1998