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Estimating the result set size of R − S

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• Range of the result set of R − S
  • Range:

    max(0, T(R)-T(S) ) ≤ T( R − S ) ≤ T(R)

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• Recommended estimate for R − S
  • Recommended:

    T( R − S ) ~= T(R) - 1/2 × T(S) Note: if T(R) - 1/2 × T(S) ≤ 0, then T( R − S ) = 0 (estimate)