'Query rewrites' diaporamas de présentation

Lecture 14: Query Optimization

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Query Optimization

Query Optimization. Query Optimization Process (simplified a bit). Parse the SQL query into a logical tree: identify distinct blocks (corresponding to nested sub-queries or views). Query rewrite phase: apply algebraic transformations to yield a cheaper plan.

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Query Optimization

sname. rating > 5. bid=100 . (Simple Nested Loops). sid=sid. Sailors. Reserves. Query Optimization. Goal:. Declarative SQL query. Imperative query execution plan:. SELECT S.sname FROM Reserves R, Sailors S WHERE R.sid=S.sid AND R.bid=100 AND S.rating>5.

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