What is SQL?
SQL (Structured Query Language) is a standard programming language used to communicate with and manage data in relational database management systems (RDBMS) like MySQL, PostgreSQL, Microsoft SQL Server, and Oracle.
What are the different types of SQL statements?
DDL, DML, DCL, TCL
What is the difference between WHERE and HAVING?
What is a primary key?
What is a foreign key?
What is the difference between INNER JOIN and LEFT JOIN?
What is the difference between DELETE, TRUNCATE, and DROP?
What is normalization? Explain its types.
What is denormalization?
What are constraints in SQL?
NOT NULL, UNIQUE, CHECK, etc.
Intermediate SQL Interview Questions
What is a subquery? How is it different from a JOIN?
What are indexes? What types are there?
What are aggregate functions in SQL?
SUM(), AVG(), COUNT(), etc.
Explain GROUP BY and ORDER BY.
What is the difference between UNION and UNION ALL?
What are views? How are they useful?
What is a stored procedure?
What is a trigger in SQL?
Explain window functions with examples.
What is the difference between correlated and non-correlated subqueries?
Advanced SQL Interview Questions
How do you optimize SQL queries for performance?
What is a CTE (Common Table Expression)? How is it used?
Explain indexing strategies.
How does SQL handle transactions?
ACID properties
What is a deadlock in SQL? How do you resolve it?
What are recursive queries? Give an example.
Explain RANK(), DENSE_RANK(), and ROW_NUMBER().
What is the difference between EXISTS and IN?
What does EXPLAIN PLAN do?
What is the difference between horizontal and vertical partitioning?
Practical Scenario-Based Questions
Write a SQL query to find the second highest salary.
Write a query to find duplicate records in a table.
Write a query to transpose rows to columns.
How do you update one table based on data from another table?
How do you retrieve the Nth highest value from a column?