Hackerrank SQL Basic Skills Certification Test Solutions Answers

Hackerrank SQL Basic Skills Certification Test Solutions Answers

The Hackerrank SQL Basic Skills Certification Test is a popular assessment designed to evaluate and validate the fundamental SQL skills of developers and data professionals. This certification is widely recognized in the industry and can significantly enhance one's credibility and employability. Here, we provide a detailed overview of the test, its structure, common types of questions, and effective strategies for solving them. In this post I will provide you Hackerrank SQL Basic Skills Certification Test Solutions.

Test Structure

The Hackerrank SQL Basic Skills Certification Test typically consists of several questions that need to be completed within a specified time frame, usually around 60 minutes. The questions are designed to test various aspects of SQL, including:

1. Basic SQL Queries: These questions assess the ability to write simple queries to retrieve data from a single table.
2. Joins: Questions that require the use of JOIN operations to combine data from multiple tables.
3. Aggregations: Problems that involve using aggregate functions like COUNT, SUM, AVG, MIN, and MAX.
4. Subqueries: Questions that require the use of nested queries to solve complex problems.
5. Date and Time Functions: Challenges that involve manipulating and querying date and time data.

Common Question Types

1. Basic SQL Queries

Example Question:
Retrieve the names of all employees in the employees table.

Solution:

SELECT name FROM employees;

2. Joins

Example Question:

List the names of all employees along with their department names. Assume employees and departments tables, where employees has a department_id column.

Solution:

SELECT e.name, d.name
FROM employees e
JOIN departments d ON e.department_id = d.id;

3. Aggregations

Example Question:
Find the total number of employees in each department.

Solution:

SELECT department_id, COUNT(*) as total_employees
FROM employees
GROUP BY department_id;

4. Subqueries

Example Question:

List the names of employees who have the highest salary in their department.

Solution:

SELECT name
FROM employees
WHERE salary = (SELECT MAX(salary) FROM employees);

5. Date and Time Functions

Example Question:
Retrieve all orders placed in the last 30 days from the orders table.

Solution:

SELECT * FROM orders
WHERE order_date >= CURRENT_DATE - INTERVAL '30 days';

Effective Strategies for Solving the Test

1. Understanding the Schema

Before diving into solving the questions, it is crucial to understand the schema of the tables involved. Familiarize yourself with the table names, column names, and relationships between tables.

2. Breaking Down the Problem

Carefully read the problem statement and break it down into smaller parts. Identify the key requirements and what the final output should look like. This will help in constructing the query step by step.

3. Writing Intermediate Queries

For complex problems, it is often helpful to write intermediate queries to verify the output at each step. This approach helps in ensuring that each part of the query is correct before combining them.

4. Using Comments

While writing SQL queries, use comments to describe each step. This practice not only helps in understanding your own logic but also makes it easier for others to review your code.

5. Testing with Sample Data

If possible, test your queries with sample data to ensure they work as expected. This can help in catching any errors or edge cases before final submission.

6. Optimizing for Performance

Although performance optimization might not be a primary concern for a basic skills test, it is good practice to write efficient queries. Avoid unnecessary joins or subqueries, and make use of indexes if applicable.

7. Practice and Review

Regular practice and review of common SQL problems can greatly improve your speed and accuracy. Utilize online resources, practice platforms, and previous Hackerrank challenges to hone your skills.

Hackerrank SQL Basic Skills Certification Test Solutions Answers

Country Codes solution

SELECT a.customer_id,a.name,concat("+",b.country_code,a.phone_number)

FROM customers as a

LEFT join country_codes as b 

ON a.country=b.country

ORDER BY a.customer_id;

Merit Reward Solutioin

SELECT ei.employee_ID, ei.name

FROM employee_information ei

JOIN last_quarter_bonus b ON b.employee_ID = ei.employee_ID

WHERE ei.division LIKE 'HR'

AND b.bonus >= 5000;

Profitable Stocks solution

SELECT a.stock_code

FROM price_today a

INNER JOIN price_tomorrow b

ON a.stock_code = b.stock_code

WHERE b.price>a.price

ORDER BY stock_code asc;

Student Advisor solution

SELECT roll_number,name

FROM student_information a

INNER JOIN faculty_information b

ON a.advisor = b.employee_ID

WHERE (b.gender = 'M' and b.salary>15000) or (b.gender = 'F' and b.salary>20000);

Student Analysis Solution

SELECT a.roll_number,a.name

FROM student_information a

INNER JOIN examination_marks b

ON a.roll_number = b.roll_number

GROUP BY b.roll_number

HAVING SUM(b.subject_one + b.subject_two + b.subject_three) < 100;

Conclusion

The Hackerrank SQL Basic Skills Certification Test is an excellent way to validate your SQL skills and enhance your professional profile. By understanding the structure of the test, familiarizing yourself with common question types, and employing effective strategies, you can confidently tackle the certification and achieve a high score. Regular practice and continuous learning are key to mastering SQL and excelling in the test.