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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( T(R), T(S) ) ≤ T( R ∪ S ) ≤ T(R) + T(S)

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• Recommended estimate for R ∪ S
  • Recommended:

    T( R ∪ S ) ~= max( T(R), T(S) ) + 1/2 × min( T(R), T(S) ) i.e.: maximum + 1/2 × (smaller size)