SQL and Database_1

What is the purpose of the SELECT statement in SQL?

• To retrieve data from a database.

• To create new tables in a database.

• To delete data from a database.

• To update existing records in a database.

Write a SQL query to retrieve all columns from a table named 'Students'.

• SELECT ALL FROM Students;

• SELECT * FROM Students;

• FETCH * FROM Students;

• GET * FROM Students;

Explain the concept of primary key in a database.

• A primary key is a unique identifier for a record in a database table, ensuring uniqueness and preventing null values.

• A primary key is used to store large binary data in a database.

• A primary key is an optional field that can contain null values.

• A primary key can be duplicated across records in a table.

What is normalization and why is it important in databases?

• Normalization is important in databases because it minimizes data redundancy, enhances data integrity, and simplifies data management.

• Normalization is only necessary for small databases.

• Normalization has no impact on data integrity.

• Normalization increases data redundancy and complexity.

Write a SQL query to find the total number of records in a table named 'Orders'.

• SELECT SUM(*) FROM Orders;

• SELECT COUNT(*) FROM Orders;

• SELECT TOTAL() FROM Orders;

• SELECT COUNT(1) FROM Orders;

What is the difference between INNER JOIN and LEFT JOIN?

• INNER JOIN returns all rows from both tables; LEFT JOIN returns only unmatched rows.

• INNER JOIN includes all rows from the left table; LEFT JOIN excludes unmatched rows from the right table.

• INNER JOIN returns all rows regardless of matches; LEFT JOIN returns only matched rows.

• INNER JOIN returns matched rows only; LEFT JOIN returns all left table rows and matched right table rows.

Write a SQL query to retrieve the names of all students who scored above 80 in a subject.

• SELECT name FROM students WHERE score < 80;

• SELECT name FROM students WHERE score >= 80;

• SELECT name FROM students WHERE score = 80;

• SELECT name FROM students WHERE score > 80;

Define the term 'foreign key' and its role in database relationships.

• A foreign key is a field that links two tables by referencing the primary key of another table, ensuring referential integrity.

• A foreign key is a field that stores data from the same table.

• A foreign key is a type of primary key.

• A foreign key is a unique identifier for a table.

What are the different normal forms in database normalization?

• 1NF, 2NF, 3NF, BCNF, 4NF, 5NF

• 1NF, 2NF, 3NF, 6NF

• 1NF, 2NF, 3NF, 4NF, 5NF, 6NF

• 1NF, 2NF, 3NF, 4NF, 7NF

Write a SQL query to update the email address of a student with ID 5.

• UPDATE students SET email = '[e-mail]' WHERE id = 5;

• UPDATE students SET email = '[e-mail]' WHERE id = 10;

• UPDATE students SET email = '[e-mail]' WHERE student_id = 5;

• UPDATE students SET email = '[e-mail]' WHERE id = 5;