Clause reduction (planner/optimizer)

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Applying the functional dependencies is fairly simple - given a list of

Applying the functional dependencies is fairly simple: given a list of

equality clauses, we compute selectivities of each clause and then use the

degree to combine them using this formula

P(a=?,b=?) = P(a=?) * (d + (1-d) * P(b=?))

Where 'd' is the degree of functionaldependence (a=>b).

Where 'd' is the degree of functionaldependency (a =>b).

With more than two equality clauses, this process happens recursively. For

example for (a,b,c) we first use (a,b=>c) to break the computation into

example for (a,b,c) we first use (a,b =>c) to break the computation into

P(a=?,b=?,c=?) = P(a=?,b=?) * (d + (1-d)*P(b=?))

P(a=?,b=?,c=?) = P(a=?,b=?) * (e + (1-e) * P(c=?))

and then apply (a=>b) the same way on P(a=?,b=?).

where 'e' is the degree of functional dependency (a,b => c); then we can

apply (a=>b) the same way on P(a=?,b=?).

Consistency of clauses