Top PostgreSQL Interview Questions for 2024 | Prep Guide

Top 50+ PostgreSQL Interview Questions and Answers for 2024

1. What does a PostgreSQL partitioned table look like?

The partitioned table is a logical structure. It is used to split a large table into smaller pieces, which are called partitions.

2. How can you avoid locking a database unnecessarily?

We can use MVCC (Multi-version concurrency control) to avoid unnecessary locking of a database.

3. What purpose does pgAdmin serve in PostgreSQL?

The pgAdmin in PostgreSQL is a data administration tool. It serves the purpose of retrieving, developing, testing, and maintaining databases.

4. What is the PostgreSQL feature called that splits a large table into smaller pieces?

It is called table partitioning.

5. What do you know about PL/Python?

PL/Python is a procedural language to which PostgreSQL provides support.

6. What methods does PostgreSQL provide to create a new database?

PostgreSQL provides the following methods to create a new database:

1. Using CREATE DATABASE, an SQL command
2. Using created a command-line executable

7. What would be the most important pieces of information you would want to include in a schema?

A schema contains tables along with data types, views, indexes, operators, sequences, and functions.

8. What are some of the different operators in PostgreSQL?

The PostgreSQL operators include: Arithmetic operators, Comparison operators, Logical operators, and Bitwise operators.

9. How can you delete a PostgreSQL database?

We can delete the database by using any one of the below options:

• Using DROP DATABASE, an SQL command
• Using dropdb a command-line executable

10. What do you think indexes are used for?

Indexes are used by the search engine to speed up data retrieval.

11. What do you think is a Cluster index's purpose?

Cluster index sorts table data rows based on their key values.

12. What do you think are database call back functions? How do they help your application?

The database call back functions are called PostgreSQL Triggers. When a specified database event occurs, the PostgreSQL Triggers are performed or invoked automatically.

13. What are the benefits of specifying data types in columns while creating a table?

Some of these benefits include consistency, compactness, validation, and performance.

14. What do you need to do to update statistics in PostgreSQL?

To update statistics in PostgreSQL, we need to use a special function called a vacuum.

15. What do you think is the disadvantage of the DROP TABLE command?

Though the DROP TABLE command has the ability to delete complete data from an existing table, the disadvantage with it is: it removes complete table structure from the database. Due to this, we need to re-create a table to store data.

16. How can you completely delete a table?

We can delete complete data from an existing table using the PostgreSQL TRUNCATE TABLE command.

17. What are the different properties of a transaction in PostgreSQL? Which acronym is used to refer to them?

The properties of a transaction in PostgreSQL include Atomicity, Consistency, Isolation, and Durability. These are referred to by the acronym, namely ACID. 

18. What purpose does the CTIDs field serve?

The CTIDs field identifies the specific physical rows in a table according to their block and offsets positions in that table.

19. Which are the commands used to control transactions in PostgreSQL?

The commands used to control transactions in PostgreSQL are BEGIN TRANSACTION, COMMIT, and ROLLBACK.

20. What are the main differences between SQL and PostgreSQL?

PostgreSQL is an advanced version of SQL. Some of the differences between these two include the following:

• Unlike SQL, views in PostgreSQL are not updatable.
• Another difference is that SQL provides computed columns; the same cannot be expected from PostgreSQL.
• Unlike SQL, in PostgreSQL, you don’t need to create a DLL to see what the code is doing.
• PostgreSQL supports dynamic actions whereas SQL doesn’t support them.

21. How is security ensured in PostgreSQL?

PostgreSQL uses SSL connections to encrypt client or server communications so that security will be ensured.

22. What is the function of the Atomicity property in PostgreSQL?

Atomicity property ensures the successful completion of all the operations in a work unit.

23. What do you think are some of the advantages of using PostgreSQL?

Some of the advantages of PostgreSQL are open-source DBMS, community support, ACID compliance, diverse indexing techniques, full-text search, a variety of replication methods, and diversified extension functions, etc.

24. How does Write-Ahead Logging help you?

The Write-Ahead Logging enhances database reliability by logging changes before any changes or updates are made to the database.

25. What are some of the important PostgreSQL administration tools?

Some of the important data administration tools supported by PostgreSQL are Psql, Pgadmin, and Phppgadmin.

26. How do you think you can store binary data in PostgreSQL?

We can store the binary data in PostgreSQL either by using bytes or by using the large object feature.

27. What do you think of the term "non-clustered index"?

In a non-clustered index, the index row order doesn’t match the order in actual data.

28. What purpose do you think table space serves in PostgreSQL?

It is a location in the disk. In this, PostgreSQL stores the data files, which contain indices and tables, etc.

29. Do you think there are any disadvantages with PostgreSQL?

 Yes. There are a few disadvantages. Some of these include the following:

• It is slower than MySQL on the performance front.
• It doesn’t have the support of a good number of open source applications when compared to MySQL.
• Since it focuses more on compatibility, changes made to improve the speed need more work.

30. What does a token in a SQL statement represent?

In a SQL Statement, a token represents an identifier, keyword, quoted identifier, special character symbol, or a constant.

31. What is the process of splitting a large table into smaller pieces called in PostgreSQL?

In PostgreSQL, the process of splitting a large table into smaller pieces is called table partitioning. It can be done using several different methods, including range partitioning, list partitioning, and hash partitioning. 

32. What are database callback functions called? What is its purpose?

Database callback functions are also known as database triggers. They are instructions automatically executed in response to specific events on a database table, such as insert, update, or delete operations. The purpose of a database trigger is to maintain data integrity, enforce business rules, and perform additional actions, such as auditing or cascading updates. 

33. What does a Cluster index do? 

A clustered index organizes the data rows in a table based on the order of the indexed columns. This means the rows with the same indexed values will be physically stored together on the storage media. This improves the performance of queries that involve those indexed columns, as the database engine can retrieve the relevant data faster.

34. What is PostgreSQL?

PostgreSQL is a free, open-source relational database management system (RDBMS) that emphasizes extensibility and SQL compliance. It is known for its robust feature set, high performance, and reliability. 

35. What are the most important features of PostgreSQL?

PostgreSQL is a powerful, open-source relational database management system known for its stability, data integrity, and robust feature set. Some of its most important features include:

• ACID compliance
• Support for advanced data types and SQL
• Multi-version concurrency control (MVCC)
• Rich indexing options

36. What are the different data types used in PostgreSQL?

In PostgreSQL, several data types can be used, including integers , floating-point numbers, character and string types, binary data, date and time types, and Boolean values.

37. What do you understand about a base directory in PostgreSQL?

In PostgreSQL, the base directory refers to the top-level directory where all data files for a specific database cluster are stored. This includes subdirectories for each database within the cluster, as well as files containing configuration settings and other metadata.

38. What do you understand about string constants in PostgreSQL?

In PostgreSQL, a string constant is a fixed sequence of characters that is enclosed in single quotes. 

39. What is the maximum size for a table in PostgreSQL?

The size for a table in PostgreSQL is 32 terabytes. 

40. What is Multi-Version Concurrency Control in PostgreSQL? Why is it used?

Multi-Version Concurrency Control (MVCC) is a technique used in PostgreSQL to allow multiple transactions to access the same data simultaneously without conflicting with each other. It is used by creating a separate version of a row for each transaction that modifies it.

41. What is the key difference between multi-version and lock models?

A multi-version model allows multiple versions of the same data to exist simultaneously, while a lock model only allows one version of the data to exist at a time, and locks the data while it is being edited.

42. What are the Indices of PostgreSQL?

Indices in PostgreSQL are used to improve the performance of data retrieval operations by providing a faster way to look up specific rows in a table. 

43. What are the tokens in PostgreSQL?

In PostgreSQL, a token is a sequence of characters that represents a single syntactic element in a SQL query. Tokens include keywords, operators, and identifiers, and are used by the PostgreSQL parser to understand the structure and meaning of a query.

44. What are some new characteristics introduced in Postgre 9.1?

PostgreSQL 9.1 introduced several new features, including support for parallel query execution, improved indexing options, and support for replication slots. It also added support for unlogged tables and improved support for JSON data types. 

45. What do you know about the history of PostgreSQL?

PostgreSQL was first released in 1996. It was developed at the University of California, Berkeley as a part of the Postgres project, and is the most popular open-source database in use today. 

46. How can you start, stop, and restart the PostgreSQL server on Windows?

To start, stop, and restart the PostgreSQL server on Windows, use the command "pg_ctl start/stop/restart -D [data directory]" in the command prompt. 

47. What is the difference between clustered index and non clustered index in PostgreSQL?

A clustered index helps in determining the physical order of data in a table, while a non-clustered index provides a faster way to look up data without affecting the physical order of the table in PostgreSQL.

48. What is the difference between PostgreSQL and MongoDB databases?

PostgreSQL is a RDBMS while MongoDB is a document-oriented NoSQL database. 

49. What do you understand about parallel queries in PostgreSQL? How does it work?

Parallel query in PostgreSQL is a feature that allows multiple parallel worker processes to work on a single query to improve performance and speed up query execution time by breaking down the query into smaller parts and processing them in parallel. 

50. What is the use of command enable-debug in PostgreSQL?

The "enable_debug" command in PostgreSQL is used to enable or disable debugging output for various subsystems of the database system.

51. What are the reserved words in PostgreSQL?

The reserved words in PostgreSQL are keywords that have a special meaning in the SQL language and cannot be used as identifiers (such as table or column names) without being quoted. 

52. What is tablespace in PostgreSQL? What is its usage?

A tablespace in PostgreSQL is a location on disk where data files of specific tables or indexes can be stored, allowing for more control over disk usage and file placement. 

53. What are the three phenomena that must be prevented between concurrent transactions in PostgreSQL?

The three phenomena that must be prevented between concurrent transactions in PostgreSQL are lost updates, dirty reads, and inconsistent reads.

54. What are the key differences between Oracle and PostgreSQL?

Oracle is a proprietary database management system while PostgreSQL is open-source

55. What do you understand about a sequence in PostgreSQL?

A sequence in PostgreSQL is a database object that generates a sequence of unique integers, which can be used as the default value for a column or as part of a primary key. 

56. What do you understand about the inverted file in PostgreSQL?

An inverted file in PostgreSQL is a data structure used to efficiently search and retrieve data from a table or index by mapping terms or keywords to the corresponding rows or documents in which they appear.

Conclusion

Getting started with PostgreSQL interview questions can be a quick trip down the easy route or a winding long road of confusion and uncertainty. That’s why we’ve put together the above Top 50+ PostgreSQL interview Questions with answers to help you with your interview.

If you are looking to enhance your software development skills further, we would highly recommend you to check out Simplilearn’s Full Stack Developer - MERN Stack. In collaboration with IBM, this course can help you hone the right skills and make you job-ready.