Approaches to Optimisation
Three main classes of techniques developed:
- algebraic (equivalences, rewriting, heuristics)
- physical (execution costs, search-based)
- semantic (application properties, heuristics)
All driven by aim of minimising (or at least reducing) "cost".
Real query optimisers use a combination of algrebraic+physical.
Semantic QO is good idea, but expensive/difficult to implement.
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