Transforming Relational Algebra Expressions
Select
Because of CNF, selects can be cascaded.
select(R, p1 and p2) = select(select(R, p1), p2)
= select(select(R, p2), p1)
This generalizes, e.g.
select(R, p1 and p2 and p3 and p4) =
select(
select(
select(
select(R, p1),
p2),
p3),
p4)
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