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Questions and Answers
What is the main function of filters in relational algebra?
What is a characteristic of relational algebra?
What is the purpose of the 'select' clause in relational algebra?
What is the notation for the select operation in relational algebra?
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What is the result of applying the select operation to a relation?
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What is the purpose of the projection operation in relational algebra?
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What is an example of a query in relational algebra?
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What is the input to relational algebra operations?
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What is the symbol used to represent the selection operation in relational algebra?
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What is the purpose of the 'where' clause in relational algebra?
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What is the result of the selection operation on a relation?
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What is the purpose of the rename operation in relational algebra?
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What is the notation for the selection operation that shows all employees who belong to department number 5?
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What is the combination of operations that normally happens in relational algebra?
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Study Notes
Relational Algebra
- Relational algebra is a procedural language that represents a query in a mathematical way.
- Relations are the inputs, and resulting relations are the outputs.
Select Operation (σ)
- The select operation filters the tuples of a resulting relation R based on the condition provided.
- It is commutative.
- Example: σcondition(relation)
- Example 1: Show all employees who belong to department number 5. σdepartment=5(employee)
- Example 2: Show all employees whose monthly salary is above Php30,000 and belong to department 3, 4, and 5. σsalary > 30000 and department >=3 and department
Project Operation (π)
- The project operation filters the attributes/columns of a resulting relation R based on the attributes listed.
- It is not entirely commutative, but proper use of projection makes it commutative.
- Example: πattributes(relation)
- Example: Show all first and last names of employees. πfirstname, lastname(employee)
- Example 2: Show all last names, department numbers, and monthly salaries of employees. πlastname, department, salary(employee)
Rename Operation (⍴)
- The rename operation renames a relation and/or its attributes.
- Example: ⍴new_relation(new_attributes)(old_relation)
- It is used to rename a relation and/or its attributes.
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Description
This quiz covers the basics of Relational Algebra, including filtering attributes and columns, procedural language, and relation inputs.
