Top 25+ PostgreSQL Interview Questions and Answers

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PostgreSQL is a free and powerful relational database system. It was created in the 1980s at the University of California, Berkeley. A professor named Michael Stonebraker started the project. At first, it was called POSTGRES. Later, it became PostgreSQL and is now used all over the world. Many companies and developers trust it because of its stability and advanced features. If you are applying for roles involving databases, there is a high chance you will face PostgreSQL interview questions. This blog lists 25+ commonly asked questions and answers to help you prepare smartly.

Fun Fact – PostgreSQL is used by 49% of developers worldwide, making it the most popular database.

Basic Level PostgreSQL Interview Questions

This section covers basic-level PostgreSQL interview questions and answers to help you build a strong foundation before moving to advanced topics.

1. What is PostgreSQL, and what are its key features?

PostgreSQL is an open-source object-relational database system. It supports SQL standards and offers features like ACID compliance, multi-version concurrency control (MVCC), custom data types, full-text search, and JSON support. It’s known for reliability, data integrity, and extensibility.

2. How do you create a new database and table in PostgreSQL?

To create a database, use:

CREATE DATABASE mydb;  

To create a table:

CREATE TABLE users (id SERIAL PRIMARY KEY, name TEXT);  

The SERIAL type auto-generates unique IDs.

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

• CHAR(n) is fixed-length. It pads spaces if the string is shorter.
• VARCHAR(n) is variable-length with a limit.
• TEXT is variable-length with no limit.
  Use TEXT if you don’t need length constraints.

4. How does PostgreSQL handle transactions and ensure ACID compliance?

It uses MVCC for safe concurrent transactions. Each change is recorded without locking others out. PostgreSQL follows Atomicity, Consistency, Isolation, and Durability. For example, if one query in a transaction fails, the whole block rolls back.

5. What is the purpose of the psql command-line tool?

psql is PostgreSQL’s terminal-based client. You use it to run SQL queries, scripts, and manage the database interactively or through files.

Also Read - Top 20+ Interview Questions for RDBMS with Expert Answers

PostgreSQL Interview Questions for Freshers

These interview questions on PostgreSQL are ideal for freshers looking to understand core concepts and prepare for entry-level roles.

6. What is a primary key, and how is it defined in PostgreSQL?

A primary key uniquely identifies each row in a table. It cannot be null. You define it like this:

id SERIAL PRIMARY KEY  

It automatically adds a unique constraint.

7. How do you insert data into a table using SQL?

Use the INSERT command. Example:

INSERT INTO users (name) VALUES (‘Alice’);  

This adds one row to the users table.

8. What is a foreign key, and why is it important?

A foreign key links one table to another. It keeps data consistent. For example, if you have orders that reference users, a foreign key prevents adding orders for non-existent users.

9. How can you retrieve all records from a table?

Use a simple SELECT query:

SELECT * FROM users;  

This fetches every row and column from the table.

10. What is the difference between DELETE and TRUNCATE commands?

DELETE removes selected rows and can use conditions. It logs each row change.

TRUNCATE removes all rows instantly and is faster. It doesn’t log individual deletions.

Use DELETE when you need selective removal. Use TRUNCATE for a full clean-up.

PostgreSQL Interview Questions for Experienced Professionals 

Here are some commonly asked PostgreSQL DBA interview questions for experienced professionals. 

11. Explain the concept of Multi-Version Concurrency Control (MVCC) in PostgreSQL.

MVCC allows multiple transactions to access the database without blocking each other. Each transaction sees a snapshot of the data. This avoids read locks. Updates create new row versions instead of overwriting. Old versions are cleaned up later by autovacuum.

12. How do you optimize query performance in PostgreSQL?

Start with the EXPLAIN or EXPLAIN ANALYZE command. It shows how queries are executed. Use proper indexing, avoid SELECT *, and write precise conditions. Partition large tables if needed. Keep statistics updated. Monitor slow queries using pg_stat_statements.

13. What are the different types of indexes available in PostgreSQL?

PostgreSQL supports several index types:

• B-tree: Default and used for most queries.
• Hash: Fast for equality comparisons.
• GIN: Used for arrays and full-text search.
• GiST: Supports geometric data and custom indexes.
• BRIN: Good for very large, naturally ordered tables.

14. How does PostgreSQL handle replication and high availability?

It supports streaming replication out of the box. One primary server sends WAL files to standby servers. You can set it as synchronous or asynchronous. Tools like Patroni, repmgr, and pg_auto_failover help with failover and HA setups.

15. Describe the process of performing a backup and restore in PostgreSQL.

Use pg_dump for logical backups and pg_basebackup for physical. For restore, use psql with the dump file or recover the base backup along with WAL logs. Always test backups on a staging server before production use.

Also Read - Top 50+ SQL Server Interview Questions and Answers

PostgreSQL Interview Questions for 3 Years Experienced

• What is the purpose of the EXPLAIN command in PostgreSQL?
• Describe a challenging database issue you faced and how you resolved it.
• How do you prioritize tasks when managing multiple database projects?
• How would you implement partitioning in a large PostgreSQL table?

PostgreSQL Interview Questions for 4 Years Experienced

• What are materialized views, and how do they differ from regular views?
• Share an experience where you improved database performance.
• How do you stay updated with the latest PostgreSQL features?
• Explain the steps to set up logical replication in PostgreSQL.

PostgreSQL Interview Questions for 5 Years Experienced

• What is the role of pg_stat_activity in monitoring PostgreSQL?
• Discuss a time when you had to troubleshoot a critical database outage.
• How do you mentor junior DBAs or developers in your team?
• Describe the process of setting up and managing a PostgreSQL cluster.

Advanced Level Interview Questions for PostgreSQL

These are advanced-level interview questions for PostgreSQL and their answers. 

16. How does PostgreSQL implement Write-Ahead Logging (WAL)?

PostgreSQL writes changes to WAL files before updating data files. WAL logs are stored in the pg_wal directory. This protects against crashes. After a crash, PostgreSQL replays WAL to restore changes. It also allows replication and point-in-time recovery.

17. What are the differences between synchronous and asynchronous replication?

In synchronous replication, the primary waits for at least one standby to confirm receipt of WAL before committing. This keeps data consistent but adds latency. In asynchronous mode, the primary doesn’t wait. It’s faster but risks data loss if the primary crashes before WAL is sent.

18. How do you handle deadlocks in PostgreSQL?

Deadlocks happen when two transactions block each other. PostgreSQL detects them automatically and kills one to break the cycle. To reduce risk, access tables in a consistent order, keep transactions short, and avoid holding locks longer than needed.

19. Explain the use of Common Table Expressions (CTEs) and recursive queries.

CTEs help structure complex queries and improve readability. Use them with WITH clauses. Recursive CTEs are useful for hierarchical data, like org charts. They repeatedly call themselves until a condition is met.

20. What is a TOAST table, and when is it used?

TOAST (The Oversized-Attribute Storage Technique) stores large values like big text or bytea fields. When a value exceeds a certain size, it’s stored separately in a TOAST table. This keeps the main table small and fast.

PostgreSQL Scenario Based Interview Questions

These PostgreSQL database interview questions are designed to test how you solve real-time issues in complex database environments.

21. How would you identify and resolve a slow-running query in PostgreSQL?

I would first run EXPLAIN ANALYZE to check the execution plan. Then I’d look at indexes, table size, and join methods. I also check pg_stat_statements for frequency and execution time. Sometimes, rewriting the query is faster than indexing. Autovacuum status and bloat can also affect performance.

22. Describe the steps to recover a corrupted PostgreSQL database.

Stop the server. If you have physical backups (pg_basebackup or file copy), restore them along with WAL files. For minor corruption, pg_resetwal might help—but it’s risky. Always check logs to isolate the corrupted table or block. For severe issues, restore to a new instance and recover data selectively.

23. How do you migrate a large database from MySQL to PostgreSQL?

I export the MySQL schema and data using tools like mysqldump or mydumper. Then I convert the schema using pgloader or ora2pg (it supports MySQL too). I test migration on staging first. Large datasets are better loaded in chunks or during low-traffic hours to avoid downtime.

24. What approach would you take to implement row-level security?

First, I enable row-level security on the table using ALTER TABLE tablename ENABLE ROW LEVEL SECURITY;. Then, I create policies with CREATE POLICY to allow or restrict access based on user identity or role. It’s ideal for multi-tenant apps where users should only see their own data.

25. How do you handle schema changes in a production environment with minimal downtime?

I plan schema changes during low-traffic periods. For critical systems, I use rolling deployments. I avoid long locks by breaking big changes into smaller ones. Adding columns with defaults is split into add-then-update. For zero downtime, I may create a new table, migrate data gradually, and then switch.

Other Important PostgreSQL Interview Questions

This section includes additional PostgreSQL interview questions that are commonly asked across various roles and experience levels.

PostgreSQL Developer Interview Questions

1. How do you write a function in PL/pgSQL?
2. What are the advantages of using window functions?
3. How do you handle exceptions in PostgreSQL functions?
4. Describe the use of triggers in PostgreSQL.

PostgreSQL Admin Interview Questions

These are common PostgreSQL administration interview questions asked in DBA roles to check your knowledge of daily admin tasks.

1. How do you configure PostgreSQL for high availability?
2. What tools do you use for monitoring PostgreSQL performance?
3. How do you manage backups and disaster recovery plans?
4. Explain the process of upgrading PostgreSQL to a newer version.

Note – Interview questions for PostgreSQL DBA often include topics like performance tuning, user management, backup strategies, and replication setup.

Also Read - Top 25+ SQL DBA Interview Questions and Answers

PostgreSQL Queries Interview Questions

1. Write a query to find the second highest salary from an employee table.
2. How do you retrieve duplicate records from a table?
3. Write a query to calculate the cumulative sum of sales per month.
4. Write a query to pivot data from rows to columns.

PostgreSQL Architecture Interview Questions

1. Describe the overall architecture of PostgreSQL.
2. What is the role of the postmaster process in PostgreSQL?
3. How does PostgreSQL handle concurrent connections?
4. How does PostgreSQL manage memory and caching?

Also Read - Top 100 SQL Query Interview Questions and Answers

Tips to Prepare for PostgreSQL Interview

Brush up core concepts, practice real SQL queries, and understand how PostgreSQL behaves under real scenarios. Here are some helpful tips to follow. 

• Learn how PostgreSQL handles data internally. Understand MVCC, WAL, and how vacuum works.
• Practice SQL using real datasets. Use sample databases like Pagila to simulate interview tasks.
• Write and debug SQL queries. Focus on JOINs, CTEs, window functions, and subqueries.
• Understand indexing well. Know when to use B-tree, GIN, or BRIN.
• Review error messages. Learn how PostgreSQL communicates query failures or lock issues.
• Look at real interview questions. Practice the common interview questions and how to answer them. 
• Set up a local PostgreSQL instance. Hands-on practice builds confidence.

Conclusion

These PostgreSQL interview questions cover the core concepts, real scenarios, and advanced topics asked in interviews. Practice them well and stay confident during your next tech round.

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