---

Estimating the (size of the) result set of a projection (π)

---

• Estimating S = π_a(R)
  • Recall:

    π does not remove duplicate values !!!

    ---

    ---

  • Estimating the size of S = π_attrs(R):

    T( πattrs(R) ) = T(R) // Number of tuples is unchanged size(project attrs) B( πattrs(R) ) ~= -------------------- × B(R) size(tuple)