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Questions and Answers
What is the main function of filters in relational algebra?
What is the main function of filters in relational algebra?
- To filter attributes/columns of a resulting relation (correct)
- To aggregate values in a relation
- To sort tuples in a relation
- To combine multiple relations
What is a characteristic of relational algebra?
What is a characteristic of relational algebra?
- Commutative and procedural
- Non-commutative and procedural (correct)
- Commutative and declarative
- Non-commutative and declarative
What is the purpose of the 'select' clause in relational algebra?
What is the purpose of the 'select' clause in relational algebra?
- To combine multiple relations
- To project specific attributes from a relation (correct)
- To filter out tuples from a relation
- To sort tuples in a relation
What is the notation for the select operation in relational algebra?
What is the notation for the select operation in relational algebra?
What is the result of applying the select operation to a relation?
What is the result of applying the select operation to a relation?
What is the purpose of the projection operation in relational algebra?
What is the purpose of the projection operation in relational algebra?
What is an example of a query in relational algebra?
What is an example of a query in relational algebra?
What is the input to relational algebra operations?
What is the input to relational algebra operations?
What is the symbol used to represent the selection operation in relational algebra?
What is the symbol used to represent the selection operation in relational algebra?
What is the purpose of the 'where' clause in relational algebra?
What is the purpose of the 'where' clause in relational algebra?
What is the result of the selection operation on a relation?
What is the result of the selection operation on a relation?
What is the purpose of the rename operation in relational algebra?
What is the purpose of the rename operation in relational algebra?
What is the notation for the selection operation that shows all employees who belong to department number 5?
What is the notation for the selection operation that shows all employees who belong to department number 5?
What is the combination of operations that normally happens in relational algebra?
What is the combination of operations that normally happens in relational algebra?
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.
