[prev] 85 [next]

Estimating Selection Result Size (cont)

Estimating size of result for e.g. 

select * from Enrolment where course <> 'COMP9315';

Could estimate by using:

  • uniform distribution assumption,   r,   domain size
e.g. | V(course,Enrolment) | = 2000,   | σA<>c(E) | = r * 1999/2000


Heuristic used by some systems:   | σA<>c(R) | ≅ r