Question:
The relation schema, \( \text{Person(pid, city) \), describes the city of residence for every person uniquely identified by \( \text{pid} \). The following relational algebra operators are available: \texttt{selection}, \texttt{projection}, \texttt{cross product}, and \texttt{rename}.}
To find the list of cities where at least 3 persons reside, using the above operators, the minimum number of \texttt{cross product operations that must be used is ...........\_.}
The relation schema, \( \text{Person(pid, city) \), describes the city of residence for every person uniquely identified by \( \text{pid} \). The following relational algebra operators are available: \texttt{selection}, \texttt{projection}, \texttt{cross product}, and \texttt{rename}.}
To find the list of cities where at least 3 persons reside, using the above operators, the minimum number of \texttt{cross product operations that must be used is ...........\_.}
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Cross product is used in relational algebra to combine rows from two tables. Use it judiciously for solving cardinality constraints.
Updated On: Jan 23, 2025
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The Correct Option is B
Solution and Explanation
The problem requires finding cities where at least 3 people reside. This can be accomplished as follows:
1. Use \texttt{selection} and \texttt{projection} to create a list of \( \text{city} \) values.
2. Perform \texttt{cross product} operations to create all combinations of rows for a given city, ensuring at least 3 unique entries for each city.
The minimum number of \texttt{cross product} operations required to verify at least 3 people in each city is 2. Final Answer: \[ \boxed{\text{(B)}} \]
1. Use \texttt{selection} and \texttt{projection} to create a list of \( \text{city} \) values.
2. Perform \texttt{cross product} operations to create all combinations of rows for a given city, ensuring at least 3 unique entries for each city.
The minimum number of \texttt{cross product} operations required to verify at least 3 people in each city is 2. Final Answer: \[ \boxed{\text{(B)}} \]
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