Why DML operations modify data in MySQL - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

What does a DML operation do?

Which of the following best describes the purpose of Data Manipulation Language (DML) operations in a database?

A They backup and restore the entire database.

B They modify the data stored in existing tables.

C They control user access and permissions.

D They create new tables and define their structure.

💡 Hint

Think about what happens when you add, change, or remove rows in a table.

DML operations are used to insert, update, or delete data inside tables. They change the actual data stored.

❓ query_result

intermediate

Result of an UPDATE statement

Given the table employees with columns id, name, and salary, what will be the result of this query?

UPDATE employees SET salary = salary + 500 WHERE id = 3;

Assuming the employee with id = 3 had a salary of 3000 before, what will be the new salary?

A The salary for employee 3 will be 3500.

B The salary for employee 3 will be 500.

C The salary for employee 3 will be 3000.

D The query will cause a syntax error.

💡 Hint

Think about what the UPDATE statement does to the existing value.

The UPDATE adds 500 to the current salary of 3000, resulting in 3500.

📝 Syntax

advanced

Identify the syntax error in DELETE statement

Which option contains a syntax error in the DELETE statement?

DELETE FROM employees WHERE;

A DELETE FROM employees WHERE name = 'John';

B DELETE FROM employees WHERE id = 5;

C ;5 = di EREHW seeyolpme MORF ETELED

D DELETE FROM employees WHERE;

💡 Hint

Check if the WHERE clause is complete and valid.

Option D has an incomplete WHERE clause with no condition, causing a syntax error.

❓ optimization

advanced

Optimizing multiple UPDATEs

You want to increase the salary by 10% for all employees in the sales department. Which query is the most efficient?

A UPDATE employees SET salary = salary * 1.1 WHERE department = 'sales';

B UPDATE employees SET salary = salary + salary * 0.1 WHERE department = 'sales';

C UPDATE employees SET salary = salary + 10 WHERE department = 'sales';

D UPDATE employees SET salary = salary * 1.1;

💡 Hint

Consider which query updates only the needed rows and calculates the increase correctly.

Option A efficiently updates only sales employees and correctly increases salary by 10%.

🔧 Debug

expert

Why does this INSERT fail?

Consider this INSERT statement:

INSERT INTO employees (id, name, salary) VALUES (1, 'Alice');

Why does this query fail?

A Because the VALUES keyword is misspelled.

B Because the id value 1 is already used.

C Because the salary column is missing a value and has no default.

D Because the table employees does not exist.

💡 Hint

Check if all columns listed have matching values.

The INSERT lists three columns but provides only two values, causing an error due to missing salary value.