SQL (Structured Query Language) is one of the most essential skills for data analysts, developers, and Oracle Fusion Cloud professionals. Almost every technical or functional interview involving databases includes SQL questions—ranging from basics to real-world scenarios.

In this blog post, we’ll cover the 10 most important SQL interview questions that are frequently asked, along with simple explanations and examples to help you understand the concepts clearly.

1. What is SQL and why is it used?

SQL stands for Structured Query Language. It is used to store, retrieve, update, and manage data in relational databases.

SQL is used to:

• Fetch data from database tables
• Insert, update, or delete records
• Create and modify database objects
• Control access and permissions

SQL is widely used in systems like Oracle, MySQL, SQL Server, and PostgreSQL, and plays a crucial role in Oracle Fusion reporting and integrations.

2. What is the difference between WHERE and HAVING?

SELECT department_id, COUNT(*)
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 5;

3. What is the difference between DELETE, TRUNCATE, and DROP?

Key Interview Tip:
DELETE supports WHERE clause, but TRUNCATE does not.

4. What are joins? Explain different types of joins.

Joins are used to combine data from multiple tables based on a related column.

Common Join Types:

• INNER JOIN – Returns matching records
• LEFT JOIN – All records from left table
• RIGHT JOIN – All records from right table
• FULL JOIN – All records from both tables

Example:

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

5. What is the difference between INNER JOIN and LEFT JOIN?

• INNER JOIN returns only matching records from both tables.
• LEFT JOIN returns all records from the left table and matching records from the right table.

This question is extremely common in real-world SQL interviews.

6. What are primary keys and foreign keys?

• Primary Key
  • Uniquely identifies each record
  • Cannot contain NULL values
• Foreign Key
  • References a primary key in another table
  • Maintains data integrity

Example:

employees.department_id → departments.department_id

7. What is the difference between COUNT(*) and COUNT(column_name)?

• COUNT(*) → Counts all rows (including NULLs)
• COUNT(column_name) → Counts only non-NULL values

Interview Tip:
This question tests your understanding of NULL handling.

8. What is a subquery?

A subquery is a query inside another query. It can be used in:

• SELECT
• WHERE
• FROM clauses

Example:

SELECT *
FROM employees
WHERE salary > (
    SELECT AVG(salary)
    FROM employees
);

9. What is the difference between UNION and UNION ALL?

Use UNION ALL when you don’t need duplicate removal for better performance.

10. What are indexes and why are they used?

Indexes are database objects used to speed up data retrieval.

Advantages:

• Faster SELECT queries
• Improved performance for large tables

Disadvantages:

• Slower INSERT/UPDATE
• Extra storage required

Indexes are heavily used in Oracle databases and Fusion Cloud environments.

Final Thoughts

These 10 SQL interview questions cover the most important concepts that interviewers expect every SQL professional to know. If you understand these clearly and practice them regularly, you’ll be well-prepared for:

• SQL interviews
• Oracle Fusion Cloud roles
• Real-world database tasks

At GrowCloudSkills, our goal is to help you build strong fundamentals with practical clarity.

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