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CS3223 Tutorial 8

CS3223 Tutorial 8. Fan Qi fan.qi@nus.edu.sg Database Lab 1, com1 #01-08. Query Optimization. Similar to other optimization Optimize by search Two main factor: Search Space: how many candidates Evaluation function : how to judge which candidate is good. Search Space. Query Plan.

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CS3223 Tutorial 8

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  1. CS3223 Tutorial 8 Fan Qi fan.qi@nus.edu.sg Database Lab 1, com1 #01-08

  2. Query Optimization • Similar to other optimization • Optimize by search • Two main factor: • Search Space: how many candidates • Evaluation function : how to judge which candidate is good Search Space Query Plan

  3. Query Optimization • Search Space Enumeration • Relational Algebra Equivalences • Query rewrite: • View rewrite • Semantic rewrite • Subqueryflatterning

  4. Query Optimization • Evaluation function: • A.K.A cost model • Evaluate query plan based on statistical information • Assumptions: • Independence, Uniform distribution, inclusion assumption • Reduction Factor • Selectivity • Histogram: • Equiwidth • Equidepth • Number of Rows • Per Column Distinct Value • Per Column Value Distribution • Combined Column Value Distribution • Available Index • ...

  5. Query Optimization • What if we know both ? • Dynamic programming optimization • Optimal Substructure If Q is optimal, all its subquery are optimal B A D C

  6. Question 1 (A) Cost of ? First Join: Second Join:

  7. Question 1 (B) Cost of ? 137 Cost of ? 180 Cost of ? 97

  8. Question 1 (C) Implies ? A A U A B

  9. Question 2 • Equiwidth histogram with 3 buckets • 9 distinct value • Each bucket has 3 distinct values

  10. Question 3 Table Scan data pages Clustered B+ tree (age, sal) : leaf page Height: Access Methods: Hash Index on (eid) : page (uniform distribution) Unclustered B+ tree (sal) : leaf page Height: Hash Index on (age) : pages (uniform distribution)

  11. Question 3 (a) Table Scan tuples Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) 20,000 Not Applicable Hash Index on (age)

  12. Question 3 (b) Table Scan tuples Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) Not Applicable Hash Index on (age) 2,000 + 20,000

  13. Question 3 (c) Table Scan tuples Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) Not Applicable Hash Index on (age) Not Applicable

  14. Question 3 (d) Table Scan tuple Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) 2,000 + 1 Unclustered B+ tree (sal) Not Applicable Hash Index on (age) Not Applicable

  15. Question 3 (e) Table Scan tuple Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) Hash Index on (age) Not Applicable

  16. Question 3 (f) Table Scan tuple Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) Hash Index on (age) 2,000 + 20,000

  17. Question 3 (g) Table Scan tuple Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) Hash Index on (age) Not Applicable

  18. Question 3 (h) Table Scan tuples Clustered B+ tree (age, sal) Access Methods: Hash Index on (eid) Not Applicable Unclustered B+ tree (sal) Not Applicable Hash Index on (age)

  19. Thank you! Happy Good Friday & Easter !

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