[prev] 86 [next]

Exercise 12: Selection Size Estimation

Assuming that
  • all attributes have uniform distribution of data values
  • attributes are independent of each other
Give formulae for the number of expected results for

  1. select * from R where not A=k
  2. select * from R where A=k and B=j
  3. select * from R where A in (k,l,m,n)

where j, k, l, m, n are constants.

Assume: V(A,R) = 10  and V(B,R)=100  and r=1000