Database & SQL Interview Questions - Basic Level (125 Questions)

Essential SQL Practice for Beginners Ready to Win Interviews.

Instructor: Richa Sinha

Language: English

Validity Period: 365 days

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This beginner-focused course is your essential guide to mastering SQL and database fundamentals for technical interviews.

With 125 carefully selected questions, you build a solid foundation in SQL query writing, database concepts, and real-world problem solving.

Designed specifically for newcomers, this course covers everything you need to confidently answer common interview questions — from basic SELECT statements, filtering, and joins to transactions, indexing, stored procedures, and error handling. Each question is crafted to improve your understanding and prepare you for practical scenarios you’ll face in entry-level roles.

Whether you’re a student, fresh graduate, or career changer, this course will empower you to crack your first SQL interview and step confidently into the data world.

✅ Topics Covered

Category	Topics Included
SQL Basics	`SELECT`, `FROM`, `WHERE`, `ORDER BY`, `DISTINCT`, `LIMIT`
Filtering & Sorting	`WHERE` clauses, `AND`/`OR`/`NOT` logic, `BETWEEN`, `IN`, `LIKE`, `IS NULL`, `ORDER BY`
Aggregation	`COUNT`, `SUM`, `AVG`, `MIN`, `MAX`, `GROUP BY`, `HAVING`
Joins	`INNER JOIN`, `LEFT JOIN`, `RIGHT JOIN`, `FULL JOIN`
Subqueries	Single-row and multi-row subqueries, `IN`/`EXISTS` subqueries
Constraints & Keys	`PRIMARY KEY`, `FOREIGN KEY`, `UNIQUE`, `CHECK`, `NOT NULL`, `DEFAULT`
Data Types	Numeric, character, date/time, and Boolean types
Table Operations	`CREATE TABLE`, `ALTER TABLE`, `DROP TABLE`, `INSERT`, `UPDATE`, `DELETE`
Views & Aliases	`CREATE VIEW`, using aliases with `AS`
Transactions	`BEGIN`, `COMMIT`, `ROLLBACK`, ACID properties
NULL Handling	`IS NULL`, `COALESCE`, `NULLIF`
Duplicate Management	`DISTINCT`, `ROW_NUMBER()`, CTEs for duplicate removal
Indexing Basics	What indexes are, how to create them, basic optimization tips
UNION Operations	`UNION` vs `UNION ALL`, merging datasets, usage rules
Temporary Tables	Creating and using local/global temporary tables
Stored Procedures	Basic syntax, creating and calling stored procedures, input/output parameters
Error Handling	`TRY`...`CATCH` blocks, handling division by zero, logging errors
CASE & Expressions	`CASE` statements, expressions in `SELECT` and `WHERE`
Date & Time Functions	`NOW()`, `CURRENT_DATE`, `DATE_FORMAT`, filtering by date ranges
Scenario-Based Qs	Troubleshooting queries, optimizing queries, real-world interview-style challenges

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	Descriptive
		What is a database? Explain its purpose.
		Define SQL and describe its main functions.
		What is the difference between DDL and DML commands? Give examples.
		Explain the concept of primary key and foreign key in a database.
		What is a NULL value in SQL? How does it differ from zero or an empty string?
		Define what a JOIN operation is and list different types of JOINs.
		Explain the difference between CHAR and VARCHAR data types.
		What is a UNIQUE constraint? How does it differ from a PRIMARY KEY?
		Describe what a transaction is in database systems.
		What is normalization? Briefly explain the purpose of 1NF.
		What are the key differences between SQL and NoSQL databases?
		Explain the purpose and use of the WHERE clause in SQL.
		What is the default sorting order used by the ORDER BY clause?
		Describe the purpose of the GROUP BY clause.
		What is a constraint in SQL? Name at least four types.
		What are aliases in SQL? How are they useful?
		Explain the difference between INNER JOIN and LEFT JOIN.
		What is data redundancy? How does normalization help in reducing it?
		What is the difference between HAVING and WHERE clauses?
		What are aggregate functions in SQL? Provide examples.
		What is a schema in a database?
		Explain the role of a foreign key in maintaining referential integrity.
		What is the difference between TRUNCATE and DELETE commands in SQL?
		Describe the difference between IS NULL and = NULL in SQL.
		What is a view in SQL? How is it different from a table?
		Explain what a subquery is and when you would use one.
		What is a default constraint in SQL? Provide an example.
		What is data integrity and how is it maintained in SQL?
		Describe the role of indexes. How do they affect read and write operations?
		What is a composite key? When is it used?
		What is a surrogate key in a database? How does it differ from a natural key?
		Explain the purpose of the CHECK constraint in SQL.
		What is the difference between a clustered and non-clustered index?
		What is a case statement in SQL? How is it used?
		Explain the concept of cascading in foreign key relationships.
		What is the difference between an alias for a column and a table in SQL?
		Define the ACID properties in relation to transactions.
		What does the LIMIT clause do in SQL, and when would you use it?
		What is a data type? List five common SQL data types.
		What are wildcards in SQL and how are they used with the LIKE operator?
		What is the difference between UNION and UNION ALL? When should each be used?
		What happens if the number of columns in the SELECT statements in a UNION are not equal?
		Can you use ORDER BY in a UNION query? If yes, how?
		What is a temporary table in SQL, and when would you use one?
		Explain the difference between local and global temporary tables.
		What happens to a temporary table after the session is closed?
		How can you insert data from a SELECT query into a temporary table?
		What is a stored procedure in SQL?
		What are the benefits of using stored procedures over writing queries directly in applications?
		Write a basic stored procedure to retrieve employee details by department name.
		How do you call or execute a stored procedure in SQL Server or MySQL?
		What are input and output parameters in stored procedures?
		What factors should you consider when deciding which columns to index?
		What is a composite index? When is it helpful?
		How can indexing improve performance? Give an example.
		When can indexing hurt performance instead of helping?
		What are some common SQL runtime errors? How can you handle them?
		How does error handling in SQL Server work using TRY...CATCH?
		Write an example of using TRY...CATCH to handle division by zero in a query.
		Why is error logging important in stored procedures?
		What are some best practices for preventing user input errors in SQL queries?
	SQL Queries
		Write a query to delete records from Products where the Quantity is zero.
		Write a query to retrieve all employees whose LastName starts with ‘S’.
		Write an SQL query to insert a new record into the Departments table with DeptID=5 and DeptName='Marketing'.
		Write a query to select all employees ordered by HireDate descending.
		Write an SQL query to retrieve the total number of employees in each department.
		Write a query to find the maximum salary from the Employees table.
		Write a query to get the average age of customers from the Customers table.
		Write a query to retrieve employee names and salaries, where the salary is between 40,000 and 60,000.
		Write an SQL query to list all customers whose country is either ‘USA’ or ‘Canada’.
		Write a query that returns the second highest salary from the Employees table.
		Write a query to rename a column PhoneNum to ContactNumber in a table Users.
		Write an SQL query to get the current date and time from the system.
		Write a query to find duplicate email addresses in the Users table.
		Write a query to retrieve all employees who do not belong to the 'IT' department.
		Write a query to retrieve the names of customers who have not placed any orders.
		Write a query to create a table named Books with columns: BookID, Title, Author, and Price.
		Write an SQL query to retrieve employee names who joined in the year 2024.
		Write a query to show department-wise average salary using GROUP BY.
		Write an SQL query to change the name of a department from 'Finance' to 'Accounts' in the Departments table.
		Write a query to add a new column DateOfBirth (type: DATE) to the Employees table.
		Write a query to find customers whose names end with the letter ‘n’.
		Write a query to retrieve all rows from Orders where the Amount is not NULL.
		Write a query to fetch only the first 5 rows from the Products table.
		Write a query to list employees hired between two specific dates.
		Write an SQL query to retrieve all orders placed in December 2023.
		Write a query to list the name and email of customers who have a NULL phone number.
		Write an SQL query to remove duplicate rows from a table Users based on the Email field.
		Write a query to fetch the highest, lowest, and average salary from the Employees table.
		Write a query to rename the Employees table to Staff.
		Write a query to fetch products whose prices are greater than the average product price.
		Write a query to display the number of employees in each department along with the department name.
		Write a query to select only even-numbered OrderID values from the Orders table.
		Write a query to get the full names of employees by concatenating FirstName and LastName.
		Write a query to delete all rows from Logs table without removing the table itself.
		Write a query to retrieve the top 3 highest-paid employees from the Employees table.
		Write a query to calculate the total revenue from the Orders table where Status is 'Completed'.
		Write a query to list customers who have placed more than 5 orders using a GROUP BY and HAVING clause.
		Write a query to retrieve products from the Products table where the Price is higher than the average price in their category.
		Write a query to fetch employee names and their department names by joining the Employees and Departments tables.
		Write a query to find all customers who have not placed any orders in the last 6 months.
		Write a query that combines results from Customers_USA and Customers_Canada tables using UNION.
		Modify the above query to include duplicates using UNION ALL.
		Write a SQL statement to create a temporary table called #RecentOrders to store today's orders.
		Write a query to create an index on the Email column in the Users table.
	Scenario-Based
		Your manager wants to know how many employees joined after January 1, 2020, but only those in the Sales department. Describe how you would write this query.
		You have two tables, Students and Courses. Each student can enroll in multiple courses. How would you design the database schema to handle this relationship?
		A report requires showing the total sales amount per customer. Which SQL functions would you use, and how?
		Your database has a column Email which should be unique, but duplicates exist. What steps would you take to identify and fix this?
		You are asked to optimize a query that runs very slowly on a large table. What approaches would you consider?
		Your Orders table has thousands of records. Your query takes too long. What are three possible reasons, and how would you investigate?
		A client requests a report showing the number of active users per month. Which SQL clauses and functions would help you?
		You need to merge customer records from two different tables with matching email addresses. How would you approach this?
		You are asked to restrict access to only certain rows of a table for junior staff. How can SQL support this requirement?
		A database user accidentally deleted some rows. What SQL features or practices could prevent such data loss in the future?
		A client wants an audit trail of changes to the Salary column. What would you recommend implementing?
		Your team needs to enforce a rule that no employee can have a negative salary. How would you enforce this in SQL?
		The Students table sometimes returns duplicate results. What SQL technique can be used to eliminate duplicates?
		Your Products table has no primary key and allows duplicate records. What would be your approach to fixing the design?
		You are creating a login system that checks usernames and passwords. What are some security-related best practices when storing such data in a database?
		You’re given a list of email addresses from users. Some are in uppercase and some lowercase. How would you ensure case-insensitive filtering in a query?
		A customer complains that their data was not saved. What SQL operations and database practices might prevent such issues?
		Your application inserts duplicate records during network errors. How can SQL handle this problem safely?
		The same product has different prices listed in multiple rows. How would you write a query to find these inconsistencies?
		You want to track when and who last modified a record in the Products table. What would you add to your schema to support this?

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Database & SQL Interview Questions - Basic Level (125 Questions)

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