Recall & Review
beginner
What is the Selection operation in a database?
The Selection operation is a query that retrieves rows from a table that satisfy a specific condition. It filters data based on criteria.
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beginner
Which symbol is commonly used to represent the Selection operation in relational algebra?
The Selection operation is represented by the Greek letter sigma (σ) in relational algebra.
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intermediate
How does Selection differ from Projection in database operations?
Selection filters rows based on conditions, while Projection selects specific columns from a table.
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beginner
Give an example of a Selection operation condition.
An example condition: σ (age > 30) selects all rows where the age column is greater than 30.
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beginner
What is the result of a Selection operation?
The result is a subset of the original table containing only rows that meet the selection criteria, with all columns intact.
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What does the Selection operation do in a database?
✗ Incorrect
Selection filters rows that satisfy a given condition.
Which symbol represents the Selection operation in relational algebra?
✗ Incorrect
Sigma (σ) is used for Selection; Pi (π) is for Projection.
If you want to get all employees with salary > 5000, which operation would you use?
✗ Incorrect
Selection filters rows based on conditions like salary > 5000.
What does Selection operation return?
✗ Incorrect
Selection returns rows that meet the condition, keeping all columns.
Which of these is NOT true about Selection operation?
✗ Incorrect
Selection does not change columns; it only filters rows.
Explain the Selection operation and how it is used in databases.
Think about how you pick certain records from a list based on a rule.
You got /4 concepts.
Describe the difference between Selection and Projection operations.
One picks rows, the other picks columns.
You got /4 concepts.