Transforming Relational Algebra Expressions
Query optimization is:
- A series of transformations of relational algebra expressions,
- Guided by a cost model.
There are two kinds of transformations:
- Substitute one implementation for
another. E.g. replace SelectScan
by SelectIndex.
- Rewrite part of the query plan based on an
equivalence. E.g.
select(
join(R, S),
predicate on R)
is equivalent to:
join(
select(R, predicate on R),
S)
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