GATE CS 2021 Set 1 — Question 33
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Databases → Relational Model → Selection & Projection
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Question
A relation in a relational database has 1200 tuples. The attribute has integer values ranging from 6 to 20, and the attribute has integer values ranging from 1 to 20. Assume that the attributes and are independently distributed.The estimated number of tuples in the output of is ___________.
Correct answer
819 to 820
Solution
Total number of tuples .
Attribute ranges from 6 to 20. Total distinct values = .
Attribute ranges from 1 to 20. Total distinct values = .
Probability (values are 11, 12, ..., 20).
Probability .
Since and are independent, the probability of the disjunction is:
.
Estimated number of tuples = .
Attribute ranges from 6 to 20. Total distinct values = .
Attribute ranges from 1 to 20. Total distinct values = .
Probability (values are 11, 12, ..., 20).
Probability .
Since and are independent, the probability of the disjunction is:
.
Estimated number of tuples = .
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