ADB Lecture 3

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Trying not to kill myself pt. 3

Last updated 1:43 AM on 6/6/26
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4 Terms

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What are the steps of SQL Query Execution?

  1. parsing (checking syntax, checks if it exists)

  2. Translation to internal form (converts to relational algebra)

  3. Optimisation ( chooses best execution plan)

  4. Execution (retrieve results)

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what does σ and π define in [ π_name (σ_age > 20 (Students) ] ?

σ (Selection) → filter rows

π (Projection) → select matching columns

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What are the common types of Transformations in Relational Algebra?

Select Pushdown (moves filtering operations as early as possible)

projection pushdown( sum early)

Join reordering (The optimizer may change the order of joins)

4
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Most expensive query?

Join queries: Nested loop joins, merge joins, hash join