*Top 40 SQL Interview Questions You Must Know* *Basics of SQL* 1️⃣ What is SQL? 2️⃣ What is a database? 3️⃣ What are the main types of SQL commands? 4️⃣ What is the difference between CHAR and VARCHAR2 data types? 5️⃣ What is a primary key? 6️⃣ What is a foreign key? 7️⃣ What is the purpose of the DEFAULT constraint? *Database Design & Normalization* 8️⃣ What is normalization in databases? 9️⃣ What is denormalization, and when is it used? *SQL Queries & Functions* 🔟 What is a query in SQL? 1️⃣1️⃣ What are the different operators available in SQL? 1️⃣2️⃣ What is a view in SQL? *Constraints & Joins* 1️⃣3️⃣ What is the purpose of the UNIQUE constraint? 1️⃣4️⃣ What are the different types of joins in SQL? 1️⃣5️⃣ What is the difference between INNER JOIN and OUTER JOIN? *Aggregations & Subqueries* 1️⃣6️⃣ What is the purpose of the GROUP BY clause? 1️⃣7️⃣ What are aggregate functions in SQL? 1️⃣8️⃣ What is a subquery? *Filtering & Indexing* 1️⃣9️⃣ What is the difference between the WHERE and HAVING clauses? 2️⃣0️⃣ What are indexes, and why are they used? *Data Manipulation & Optimization* 2️⃣1️⃣ What is the difference between DELETE and TRUNCATE commands? 2️⃣2️⃣ What is the purpose of the SQL ORDER BY clause? *SQL vs NoSQL* 2️⃣3️⃣ What are the differences between SQL and NoSQL databases? *Database Objects & Constraints* 2️⃣4️⃣ What is a table in SQL? 2️⃣5️⃣ What are the types of constraints in SQL? 2️⃣6️⃣ What is a cursor in SQL? 2️⃣7️⃣ What is a trigger in SQL? *SQL Statements* 2️⃣8️⃣ What is the purpose of the SQL SELECT statement? 2️⃣9️⃣ What are NULL values in SQL? 3️⃣0️⃣ What is a stored procedure? *DDL & DML Commands* 3️⃣1️⃣ What is the difference between DDL and DML commands? 3️⃣2️⃣ What is the purpose of the ALTER command in SQL? *Advanced SQL Concepts* 3️⃣3️⃣ What is a composite primary key? 3️⃣4️⃣ How is data integrity maintained in SQL databases? 3️⃣5️⃣ What are the advantages of using stored procedures? *Set Operations & Case Handling* 3️⃣6️⃣ What is a UNION operation, and how is it used? 3️⃣7️⃣ What is the difference between UNION and UNION ALL? 3️⃣8️⃣ How does the CASE statement work in SQL? *Functions & Special Operations* 3️⃣9️⃣ What are scalar functions in SQL? 4️⃣0️⃣ What is the purpose of the COALESCE function?