SQL Beginner Interview Preparation

 Level             Type

    Beginner                      Basics (Database, Tables, Basic Queries)

📌 Key Topics You Must Prepare for SQL:

  • SQL Basics – What is SQL, Commands (DDL, DML, DCL, TCL, DQL)

  • Tables and Keys – Primary Key, Foreign Key, Composite Key

  • Basic Queries – SELECT, WHERE, ORDER BY, GROUP BY, HAVING

  • Joins – INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN

  • Subqueries – Simple and Correlated

  • Constraints – NOT NULL, UNIQUE, CHECK, DEFAULT

  • Normalization – 1NF, 2NF, 3NF

  • Indexes – Clustered, Non-Clustered

  • Transactions – COMMIT, ROLLBACK, SAVEPOINT, Isolation Levels

  • Views – Virtual tables using SELECT queries

  • Stored Procedures, Functions, and Triggers

  • Optimization Techniques – Indexing, Query Tuning

  • Window Functions – ROW_NUMBER(), RANK(), DENSE_RANK()

  • Backup and Restore of Databases

  • Common Functions – COALESCE(), CASE WHEN, Aggregate Functions (SUM, AVG, COUNT)

🎯 Bonus Tips for SQL Preparation:

  • ✍️ Practice SQL Queries daily on live editors like LeetCode SQL Playground or W3Schools SQL Tryit Editor.

  • 🗂️ Create a Mini Project: A simple "Library Management System" (Books, Students, Issue, Return tables).

  • 🔥 Write Subqueries and Joins regularly; almost every company asks them.

  • 🚀 Learn indexing and optimization tricks — it makes you look senior even at fresher level!

  • 📄 Revise Important Definitions like Primary Key, Foreign Key, Transactions, Joins — you can quickly answer theory questions if needed.

  • 🎯 Mock Interview Practice: Try explaining queries out loud to yourself — this improves your real interview performance.

  • 📊 Understand Execution Plan (EXPLAIN keyword in MySQL) to understand query performance.


1. What is SQL?
➤ SQL (Structured Query Language) is used to manage and manipulate relational databases.

2. What are the different types of SQL commands?
➤ DDL (CREATE, ALTER), DML (INSERT, UPDATE, DELETE), DQL (SELECT), DCL (GRANT, REVOKE), TCL (COMMIT, ROLLBACK).

3. What is a primary key?
➤ A column that uniquely identifies each row in a table.

4. What is a foreign key?
➤ A key that is used to link two tables together.

5. What is the difference between DELETE and TRUNCATE?
➤ DELETE removes rows one by one, TRUNCATE removes all rows instantly.

6. What is a JOIN in SQL?
➤ JOIN is used to combine rows from two or more tables based on related columns.

7. What are the types of JOINs?
➤ INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN.

8. What is the difference between WHERE and HAVING?
➤ WHERE filters rows before grouping, HAVING filters after grouping.

9. What is a NULL value?
➤ NULL represents missing or unknown data.

10. How do you retrieve unique values?
➤ Using the DISTINCT keyword.

11. What is a constraint in SQL?
➤ Constraints define rules for data in a table like NOT NULL, UNIQUE, PRIMARY KEY.

12. What is normalization?
➤ Process of organizing data to reduce redundancy.

13. What is denormalization?
➤ Adding redundancy to improve read performance.

14. What is an index in SQL?
➤ Index improves the speed of data retrieval.

15. What is the default sorting order of ORDER BY clause?
➤ Ascending (ASC).

16. How to sort data in descending order?
➤ Using ORDER BY column_name DESC.

17. How to fetch the top N records?
➤ Using LIMIT (MySQL) or TOP (SQL Server).

18. What is a view in SQL?
➤ A virtual table created from a query.

19. What is a subquery?
➤ A query nested inside another query.

20. What is the use of GROUP BY?
➤ GROUP BY groups rows sharing a property so that aggregate functions can be applied.


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