题目
题目

INFO20003_2025_SM2 Exam: Database Systems (INFO20003_2025_SM2)- Requires Respondus LockDown Browser

匹配题

Single Relation Plan A Compute the estimated result size for the query, and the reduction factor of each filter.   1: RF(establishmentYear) 2: RF(postcode) 3: Result Size (tuples)

选项
A.20
B.5
C.400
D.3/4 (0.75)
E.1
F.[Select this if none of the other options are correct]
G.1/5 (0.2)
H.1/20 (0.05)
I.0.01
J.1/4 (0.25)
K.10
L.500
M.1/2 (0.5)
N.0.1
O.2
P.1/200 (0.005)
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标准答案
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思路分析
We are given a matching_question with three targets: RF(establishmentYear), RF(postcode), and Result Size (tuples). The provided correct matches are: RF(establishmentYear) → 1/5 (0.2), RF(postcode) → 1/200 (0.005), Result Size (tuples) → 1. Option-by-option analysis: Option 1: 20 - This value is not correct for any of the three targets. It could represent a crude cardinality count, but it does not align with the given reductions or final result size in the provided solution. Option 2: 5 - Like option 1, this numeric value does not match any of the specified reductions (0.2, 0.005) or the final result size (1). It seems to be an arbitrary small integer that......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)

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? 

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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