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Varieties of Selection (cont)

One-dimensional selection queries = condition on single attribute.
  • one: select * from R where k = val

    where k is a unique attribute and val is a constant

  • pmr: select * from R where k = val

    where k is non-unique and val is a constant

  • range: select * from R where k ≥ lo and k ≤ hi

    where k is any attribute and lo and hi are constants

    either lo or hi may be omitted for open-ended range