Selection operation implementation in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Selection Operation in Relational Algebra

Which of the following best describes the selection operation in relational algebra?

A It filters rows from a table based on a specified condition.

B It combines two tables by matching rows based on a common attribute.

C It rearranges the columns of a table in a specified order.

D It creates a new table by adding columns from two tables.

💡 Hint

Think about how you pick certain rows from a table based on a rule.

The selection operation chooses rows from a table that satisfy a given condition, effectively filtering the data.

📋 Factual

intermediate

SQL Equivalent of Selection Operation

Which SQL clause is used to perform the selection operation on a table?

A GROUP BY

B ORDER BY

C WHERE

D HAVING

💡 Hint

This clause filters rows before grouping or ordering.

The WHERE clause filters rows in SQL, similar to the selection operation in relational algebra.

🚀 Application

advanced

Result of Selection Operation with Multiple Conditions

Given a table Employees with columns id, name, and salary, what is the result of the selection operation with condition salary > 50000 AND name LIKE 'J%'?

DBMS Theory

SELECT * FROM Employees WHERE salary > 50000 AND name LIKE 'J%';

A All employees with salary above 50000 regardless of name.

B All employees with salary above 50000 or names starting with 'J'.

C All employees with salary below 50000 and names starting with 'J'.

D All employees with salary above 50000 whose names start with 'J'.

💡 Hint

AND means both conditions must be true.

The selection filters rows where both salary is greater than 50000 and the name starts with 'J'.

🔍 Analysis

advanced

Effect of Selection Operation on Table Size

If a selection operation is applied on a table with 1000 rows using a condition that matches 10% of the rows, how many rows will the resulting table have?

A 100 rows

B 10 rows

C 900 rows

D 1000 rows

💡 Hint

Calculate 10% of 1000.

The selection filters rows, so only 10% of 1000 rows remain, which is 100 rows.

❓ Reasoning

expert

Identifying the Correct Selection Query Output

Consider a table Products with columns product_id, category, and price. Which query will return all products in the 'Electronics' category priced below 300?

A SELECT * FROM Products WHERE category = 'Electronics' OR price < 300;

B SELECT * FROM Products WHERE category = 'Electronics' AND price < 300;

C SELECT * FROM Products WHERE category = 'Electronics' AND price > 300;

D SELECT * FROM Products WHERE category != 'Electronics' AND price < 300;

💡 Hint

Both conditions must be true for selection.

Only option B correctly filters products that are in 'Electronics' and priced below 300.