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Translating SQL Queries into Relational Algebra

Query Blocks

The first heuristic applies very early: Decompose a query into query blocks.

Optimize the blocks independently, and then combine the resulting execution plans.

A query block is composed of the following:

• select
• from
• where
• group by
• having
• order by : Outermost query only.

We are going to only discuss plans involving select, from, where and order by.

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