CSC 4402 20091123

CSC 4402 20091123 - equivalence rules 2 Annotate resultant...

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CSC 4402 11/23/2009 Page 1 of 1 Chapter 14 Focus on sections 1, 2 and 4. Main objective: to select the most efficient way/plan to evaluate a given query (or relational algebra expression) Optimization at different levels: At the relational algebra level At the more detailed level – different algorithms for implementing RA operators (join, etc.) Optimization methods: Cost-based Heuristics-based Steps in cost-based query optimization 1. Generate logically equivalent expressions using
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Unformatted text preview: equivalence rules 2. Annotate resultant expressions to get alternative query plans 3. Choose the cheapest plan based on estimated cost Two relational algebra expressions are said to be equivalent if the two expressions generate the same set of tuples on every legal database instance. Note: the order of tuples is irrelevant. Read the equivalence rules on slide 14.8 – 14.13. Rule 7b is very important and is likely to be on the test....
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