题目
题目

COMP90050_2025_SM2 Quiz 2

多项选择题

Select all the options from the following that are steps or tasks of a query optimizer. You need to choose multiple options if they are the answers.

选项
A.Generate different alternative query plans
B.Estimate the costs of the alternative query plans
C.Generate logically equivalent expressions of the query
D.Choose the cheapest plan based on estimated cost
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标准答案
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思路分析
To approach this question, I will evaluate what a query optimizer typically does and map each option to that process. Option 1: Generate different alternative query plans. This is a core activity of the optimizer: it explo......Login to view full explanation

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Query Optimisation Plan 2  Compute the following results for the below Plan 2:  The result size of the selection on vendor in pages (marked as 'A' in the diagram) The result size of the child join in pages (marked as 'B' in the diagram) The cost of the selection on vendor in I/Os (note this also accounts for the index access cost as well) (marked as 'C' in the diagram) The cost of the child join in I/Os (marked as 'D' in the diagram) The cost of the parent join in I/Os (marked as 'E' in the diagram)   Figure 3.3.2: PLAN 2. 1: The result size of the selection on Vendor in PAGES (marked as 'A' in the diagram) 2: The result size of the child join in PAGES (marked as 'B' in the diagram) 3: The cost of the selection on Vendor in I/Os (note this also accounts for the index access cost as well) (marked as 'C' in the diagram) 4: The cost of the child join in I/Os (marked as 'D' in the diagram) 5: The cost of the parent join in I/Os (marked as 'E' in the diagram)

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Single Relation Plan C What would happen if our query changed and became:  SELECT hotspotID FROM hotspot WHERE postcode = 2600 AND establishmentYear > 2020 AND establishmentYear < 2022; Assuming that the unclustered B+tree index on establishmentYear from the previous question is the only index available, would the cost of the best plan change? 

Single Relation Plan B Compute the estimated cost of plan alternatives, assuming that an unclustered B+tree index on (establishmentYear) is the only index available. Suppose there are 10 index pages.  Give the lowest (estimated) cost in I/Os after considering all access methods available.  Round up any decimals to the nearest integer (e.g., 3.3 rounds up to 4).

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