100 Must-Know SQL Interview Questions and Answers 2024

SQL Fundamentals

1.
What is SQL and what is it used for?
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2.
Describe the difference between SQL and NoSQL databases.
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3.
What are the different types of SQL commands?
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4.
Explain the purpose of the SELECT statement.
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5.
What is the difference between WHERE and HAVING clauses?
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6.
Define what a JOIN is in SQL and list its types.
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7.
What is a primary key in a database?
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8.
Explain what a foreign key is and how it is used.
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9.
How can you prevent SQL injections?
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10.
What is normalization? Explain with examples.
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11.
Describe the concept of denormalization and when you would use it.
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12.
What are indexes and how can they improve query performance?
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13.
Explain the purpose of the GROUP BY clause.
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14.
What is a subquery, and when would you use one?
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15.
Describe the functions of the ORDER BY clause.
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16.
What are aggregate functions in SQL?
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17.
Explain the differences between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
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18.
How do you insert a new row into a database table?
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19.
Explain how to update records in a database table.
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20.
What is a SQL View and what are its advantages?
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SQL Data Types and Operators

21.
List the different data types available in SQL.
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22.
What are the differences between CHAR, VARCHAR, and TEXT data types?
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23.
How do you use the BETWEEN operator in SQL?
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24.
Describe the use of the IN operator.
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25.
Explain the use of wildcard characters in SQL.
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26.
What is the purpose of the LIKE operator?
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27.
How do you handle NULL values in SQL?
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28.
What does the COALESCE function do?
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29.
What is the difference between UNION and UNION ALL?
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30.
Describe the use of arithmetic operators in SQL queries.
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SQL Advanced Queries

31.
Explain how to use the CASE statement in SQL.
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32.
How would you perform a self JOIN?
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33.
What is a cross JOIN and when would you use it?
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34.
How to implement pagination in SQL queries?
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35.
Explain the concept of Common Table Expressions (CTEs) and recursive CTEs.
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36.
What are window functions and how are they used?
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37.
How can you concatenate column values in SQL?
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38.
What is the PIVOT operation and how would you apply it?
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39.
Explain the process of combining a query that uses a GROUP BY with one that uses ORDER BY.
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40.
How would you find duplicate records in a table?
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Database Design & Architecture

41.
What is the Entity-Relationship Model?
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42.
Explain the different types of database schema.
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43.
What are Stored Procedures and how are they beneficial?
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44.
What is a trigger in SQL and when should it be used?
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45.
Describe the concept of ACID in databases.
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46.
What is database sharding?
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47.
How do database indexes work and what types are there?
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48.
Describe the process of data warehousing.
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49.
Explain the difference between OLTP and OLAP systems.
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50.
What are materialized views and how do they differ from standard views?
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SQL Optimization and Performance

51.
How do you identify and optimize slow-running queries?
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52.
What is query execution plan in SQL?
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53.
Explain how to use EXPLAIN or EXPLAIN ANALYZE.
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54.
How can indexing affect performance both positively and negatively?
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55.
Describe how to measure the performance of SQL queries.
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56.
How would you rewrite a query to improve its performance?
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57.
What are partitioned tables and how can they optimize performance?
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SQL Security

58.
How do you implement database encryption in SQL?
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59.
What are roles and how do they manage database access?
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60.
Explain the concept of row-level security.
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61.
Describe how to create and use user-defined functions (UDFs).
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SQL Functions and Expressions

62.
Describe scalar-valued and table-valued functions.
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63.
How would you define a stored procedure with input and output parameters?
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64.
What is the difference between a function and a stored procedure?
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65.
How do you use the CAST and CONVERT functions?
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Transaction Control and Locking

66.
What is a database transaction?
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67.
Explain the concept of locking and its types in SQL databases.
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68.
What are the properties of transactions?
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69.
How do you manage transaction isolation levels?
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70.
What does it mean to commit or roll back a transaction?
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SQL and Modern Data Ecosystems

71.
How can SQL be integrated with big data technologies?
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72.
Discuss the interoperability of SQL with cloud-based data stores.
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73.
What is Data Lake and how can SQL interact with it?
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74.
Explain the interaction between SQL and NoSQL within the same application.
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75.
How does SQL work within a microservices architecture?
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SQL Best Practices and Standards

76.
What are some common SQL coding practices you follow?
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77.
How can you ensure the portability of SQL scripts across different database systems?
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78.
What methods do you use for version controlling SQL scripts?
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79.
What are the benefits of using stored procedures instead of embedding SQL queries in code?
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80.
How do you document SQL code effectively?
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Analytical SQL Questions

81.
How would you find the Nth highest salary from a table?
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82.
How do you count the number of occurrences of a specific value in a column?
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83.
How can you calculate running totals in SQL?
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84.
Explain how to reverse the contents of a column without using a reverse function.
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85.
What approach do you use for creating a calendar table, and what are its uses?
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Data Manipulation and ETL

86.
What is the process of Extract, Transform, Load (ETL)?
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87.
How do you import/export data from/to a flat file using SQL?
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88.
Explain the steps for a basic ETL process in a data warehousing environment.
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89.
How do you cleanse and format data using SQL queries?
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90.
What tools do you use for automating data import/export routines?
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Domain-Specific SQL Scenarios

91.
How would you model a many-to-many relationship in SQL?
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92.
Describe how to manage hierarchical data in SQL.
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93.
How would you approach writing SQL queries for a reporting application?
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94.
Explain how to handle temporal data and time zones in SQL.
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95.
How do you use SQL in financial applications for risk and portfolio analysis?
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Troubleshooting and Debugging

96.
What steps do you take to troubleshoot a failed SQL query?
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97.
How can you recover data from a corrupt SQL database?
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98.
What methods do you employ to ensure data integrity?
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99.
How do you decipher and resolve deadlocks in SQL?
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Advanced Data Analysis in SQL

100.
Explain how to use SQL for predictive analysis and machine learning purposes.
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100 SQL interview questions

What is SQL and what is it used for?

Describe the difference between SQL and NoSQL databases.

What are the different types of SQL commands?

Explain the purpose of the SELECT statement.

What is the difference between WHERE and HAVING clauses?

Define what a JOIN is in SQL and list its types.

What is a primary key in a database?

Explain what a foreign key is and how it is used.

How can you prevent SQL injections?

What is normalization? Explain with examples.

Describe the concept of denormalization and when you would use it.

What are indexes and how can they improve query performance?

Explain the purpose of the GROUP BY clause.

What is a subquery, and when would you use one?

Describe the functions of the ORDER BY clause.

What are aggregate functions in SQL?

Explain the differences between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.

How do you insert a new row into a database table?

Explain how to update records in a database table.

What is a SQL View and what are its advantages?

List the different data types available in SQL.

What are the differences between CHAR, VARCHAR, and TEXT data types?

How do you use the BETWEEN operator in SQL?

Describe the use of the IN operator.

Explain the use of wildcard characters in SQL.

What is the purpose of the LIKE operator?

How do you handle NULL values in SQL?

What does the COALESCE function do?

What is the difference between UNION and UNION ALL?

Describe the use of arithmetic operators in SQL queries.

Explain how to use the CASE statement in SQL.

How would you perform a self JOIN?

What is a cross JOIN and when would you use it?

How to implement pagination in SQL queries?

Explain the concept of Common Table Expressions (CTEs) and recursive CTEs.

What are window functions and how are they used?

How can you concatenate column values in SQL?

What is the PIVOT operation and how would you apply it?

Explain the process of combining a query that uses a GROUP BY with one that uses ORDER BY.

How would you find duplicate records in a table?

What is the Entity-Relationship Model?

Explain the different types of database schema.

What are Stored Procedures and how are they beneficial?

What is a trigger in SQL and when should it be used?

Describe the concept of ACID in databases.

What is database sharding?

How do database indexes work and what types are there?

Describe the process of data warehousing.

Explain the difference between OLTP and OLAP systems.

What are materialized views and how do they differ from standard views?

How do you identify and optimize slow-running queries?

What is query execution plan in SQL?

Explain how to use EXPLAIN or EXPLAIN ANALYZE.

How can indexing affect performance both positively and negatively?

Describe how to measure the performance of SQL queries.

How would you rewrite a query to improve its performance?

What are partitioned tables and how can they optimize performance?

How do you implement database encryption in SQL?

What are roles and how do they manage database access?

Explain the concept of row-level security.

Describe how to create and use user-defined functions (UDFs).

Describe scalar-valued and table-valued functions.

How would you define a stored procedure with input and output parameters?

What is the difference between a function and a stored procedure?

How do you use the CAST and CONVERT functions?

What is a database transaction?

Explain the concept of locking and its types in SQL databases.

What are the properties of transactions?

How do you manage transaction isolation levels?

What does it mean to commit or roll back a transaction?

How can SQL be integrated with big data technologies?

Discuss the interoperability of SQL with cloud-based data stores.

What is Data Lake and how can SQL interact with it?

Explain the interaction between SQL and NoSQL within the same application.

How does SQL work within a microservices architecture?

What are some common SQL coding practices you follow?

How can you ensure the portability of SQL scripts across different database systems?