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.多项选择题

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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The cut-and-try approach will always identify the aggregate plan with the lowest overall cost.

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)

Query Optimisation Plan 1  Compute the following results for the below Plan 1:  The result size of the child join in pages (marked as 'A' in the diagram) The cost of the child join in I/Os (marked as 'B' in the diagram).  The cost of the parent join in I/Os (marked as 'C' in the diagram)     Figure 3.3.1: PLAN 1. 1: The result size of the child join in PAGES (marked as 'A' in the diagram) 2: The cost of the child join in I/Os (marked as 'B' in the diagram) 3: The cost of the parent join in I/Os (marked as 'C' in the diagram)

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? 

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