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sqlrelational-databaserelational-algebra

Relational Algebra - Select with no predicate

I know about relational algebra, but with regard to the select part of it, what should I say if there isn't any specific condition.

For example I have a Hotels Table and I just want to output that result.

Should I just use σ(Hotels) or do I need to put something like σALL(Hotels)???

I need your help!

Solution

  • Use an existing relation if you don't have any condition.

    Examples:

    Algebra: R

    SQL: SELECT * FROM R

    Algebra: Hotels

    SQL: SELECT * FROM Hotels

    Returns every tuple in the Hotels table that you need. (No particular order is requested or implied.)

    If you need to apply any condition only then use

    σ <selection condition> (R)