Table of contents
1.
Introduction
2.
Top 15 Beginner PostgreSQL Interview Questions
2.1.
1. Describe Postgresql.
2.2.
2. What are the features and capabilities of Postgres DB?
2.3.
3. What does PostgreSQL's Multi-Version Concurrency Control mean?
2.4.
4. What is a ctid in PostgreSQL?
2.5.
5. Provide a brief explanation of the functions in PostgreSQL?
2.6.
6. Which is superior, PostgreSQL or MySQL?
2.7.
7. Describe pgadmin?
2.8.
8. What does "Multi-version Control" mean?
2.9.
9. What does PostgreSQL table partitioning entail?
2.10.
10. What do PostgreSQL indexes do?
2.11.
11. What do PostgreSQL tokens mean?
2.12.
12. How are queries involving several databases carried out?
2.13.
13. Describe PostgreSQL Functions in detail.
2.14.
14. Explain Triggers.
2.15.
15. What kinds of Data Types does Postgresql support?
3.
15 Intermediate PostgreSQL Interview Questions
3.1.
16. Is it possible to set up a PostgreSQL server cluster with shared storage?
3.2.
17. What exactly are string constants?
3.3.
18. What Different Postgresql Enhancements Are Made To The Straight Relational Data Model?
3.4.
19. How are Postgresql stats updated?
3.5.
20. What contrasts exist between Postgresql and NoSQL?
3.6.
21. What Has Changed in Postgre 9.1?
3.7.
22. Is Postgresql a Cloud-based Database?
3.8.
23. How Do Oracle/db2/ms SQL Server/Informix and Postgresql Compare?
3.9.
24. What are Connector Libraries?
3.10.
25. What is Full-Text Search? Does Postgresql offer support for it?
3.11.
26. What do you understand by inverted files in PostgreSQL?
3.12.
27. What drawbacks does PostgreSQL have?
3.13.
28. What is a Foreign Data Wrapper (FDW) in PostgreSQL, and how can it be used for data integration?
3.14.
29. What are Materialized Views in PostgreSQL, and how do they differ from regular views?
3.15.
30. What are Advisory Locks in PostgreSQL, and how can they be used for application-level locking?
4.
15 Advanced and PostgreSQL Interview Questions
4.1.
31. What is a Foreign Data Wrapper (FDW) in PostgreSQL, and how can it be used for data integration?
4.2.
32. What are Materialized Views in PostgreSQL, and how do they differ from regular views?
4.3.
33. What are Advisory Locks in PostgreSQL, and how can they be used for application-level locking?
4.4.
34. Explain the concept of JSONB in PostgreSQL and its benefits.
4.5.
35. How does PostgreSQL handle concurrency with Multi-Version Concurrency Control (MVCC)?
4.6.
36. What is the significance of PostgreSQL’s WAL (Write-Ahead Logging)?
4.7.
37. How does PostgreSQL support full-text search, and what are its key features?
4.8.
38. What is the role of pg_stat_statements in PostgreSQL, and how can it be used for query optimization?
4.9.
39. How can you implement partitioning in PostgreSQL, and what are its advantages?
4.10.
40. What are the different types of indexes in PostgreSQL, and when should each be used?
4.11.
41. How do you perform replication in PostgreSQL, and what are the available methods?
4.12.
42. What is a Hot Standby in PostgreSQL, and how does it work?
4.13.
43. Explain the concept of VACUUM in PostgreSQL and why it is necessary.
4.14.
44. How does PostgreSQL handle transactional integrity, and what are the ACID properties?
4.15.
45. What are the benefits and challenges of using PostgreSQL in a cloud environment?
5.
PostgreSQL MCQs
5.1.
1. What is the default port number for PostgreSQL?
5.2.
2. Which PostgreSQL command is used to create a new database?
5.3.
3. What does the VACUUM command do in PostgreSQL?
5.4.
4. Which PostgreSQL feature allows you to execute SQL commands from a file?
5.5.
5. How do you list all the tables in a PostgreSQL database?
6.
Frequently Asked Questions
6.1.
What is the main purpose of PostgreSQL?
6.2.
What is the latest version of PostgreSQL?
6.3.
Why is PostgreSQL the most loved database?
7.
Conclusion
Last Updated: Sep 2, 2024
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PostgreSQL Interview Questions and Answers

Author Mayank Goyal
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Introduction

Object-relational database management system (ORDBMS) PostgreSQL, also referred to as Postgres, is one such technology. Initially created by the PostgreSQL Global Development Group in 1996, the stable release was made in 2018. Specifically, extensibility and standards compliance are emphasized. It manages large workloads, including those running simultaneously on macOS, Linux, and Windows, ranging from simple single-machine apps to massive Internet-facing applications with many concurrent users. To get chosen for the interview, review the wisdom jobs database of PostgreSQL interview questions and answers. Mumbai, Delhi, Bangalore, Pune, and Hyderabad are just a few cities where one can examine employment availability. Furthermore, we will be covering PostgreSQL Interview Questions that are frequently asked.

PostgreSQL Interview Questions

Here, we've included a list of a few crucial and probable interview questions. The questions can be understood with practice, diligence, and hard work. If you read through the questions, you can discover several that are asked practically universally in interviews.

Top 15 Beginner PostgreSQL Interview Questions

1. Describe Postgresql.

One of the most popular open-source databases in the world is this one. Additionally, this is utilized to make sophisticated applications. The object-relational database management system is used for this. Being familiar with Linux and UNIX can be helpful while using PostgreSQL.

2. What are the features and capabilities of Postgres DB?

The following are the main PostgreSQL features and functionalities:

  • Object-relational database.
  •  Flexibility and SQL support.
  • Flexible Application Program Interface and DB validation.
  • Procedural languages and Multi-Version Concurrency Control.
  • Client servers and WAL.

3. What does PostgreSQL's Multi-Version Concurrency Control mean?

An advanced technique used in PostgreSQL for enhancing database performance in a multi-user environment is called Multi-Version Concurrency Control (MVCC). PostgreSQL uses a multi-version environment, unlike lock models in other databases, so locks gained for reading data don't conflict with locks acquired for writing the data. Consequently, the procedure will be much quicker and more segmented.

4. What is a ctid in PostgreSQL?

Every PostgreSQL table has a ctid field. It designates the tuple location and is distinct for every record in a table. Records may be deleted with it. Remember that we should only utilize ctid if we are completely out of options for other unique identifiers.

5. Provide a brief explanation of the functions in PostgreSQL?

Functions are crucial in the server's ability to execute the code. PL/pgSQL, a native language of PostgreSQL, and other scripting languages like Perl, Python, PHP, etc., are some of the languages used to create functions. The functions' efficiency can also be improved using the statistical language PL/R.

6. Which is superior, PostgreSQL or MySQL?

MySQL is the ideal database to learn on. It is the top option for web-based programs that only need a database for transactions. However, PostgreSQL is superior in terms of features and speed. It is more frequently used for data warehousing, analysis, and executing sophisticated queries.

7. Describe pgadmin?

A feature called Pgadmin is recognized as a graphical front-end administrative tool. Free software produced under an artistic license includes this feature. The brand-new database management tool available under creative license is pgadmin iii. 

8. What does "Multi-version Control" mean?

MVCC, also known as multi-version concurrency control, prevents needless database locking. By doing this, the user's database login time is no longer delayed. When another user gains access to the content, this function or time lag appears. Records of each transaction are maintained.

9. What does PostgreSQL table partitioning entail?

Table partitioning in PostgreSQL refers to dividing a huge table into smaller portions. Through table inheritance, PostgreSQL allows list and range partitioning. Users must create each division as a child table of the master table.

10. What do PostgreSQL indexes do?

The index is a popular method for improving database performance in PostgreSQL. Compared to not having an index, it enables the database server to locate and retrieve particular rows more quickly. Additionally, it increases the overall overhead of the database system. Therefore users must apply them carefully.

The database search engine uses indexes, and specialized lookup tables, to speed up data retrieval. An index is a pointer to a particular piece of data in a table.

11. What do PostgreSQL tokens mean?

A token can be a word, a phrase, a quote, a literal (or constant), or a unique representation of a person's personality. Whitespace (space, tab, newline) is typically used to separate tokens. However, it is not required if there is no ambiguity (which is usually only the case if a unique persona is adjoining to some other token type).

12. How are queries involving several databases carried out?

There is no alternative way to query a database besides one already existing. A cross-database query's behavior for PostgreSQL is unclear because it loads database-specific system catalogs.

However, cross-database queries using function calls are supported by contrib or dblink. However, clients can also establish concurrent connections to various databases and combine the outcomes.

13. Describe PostgreSQL Functions in detail.

Functions are crucial because they provide the server's ability to execute code. One of the languages, PL/pgSQL, the native language of PostgreSQL, is capable of programming functions for effective use. Many languages, such as PHP, Perl, Python, etc., support scripting languages. Another option is to utilize the statistical language PL/R. 

14. Explain Triggers.

You can start an event by using a SQL query. INSERT and UPDATE queries can be used to activate triggers. Tables may be equipped with these. Multiple triggers may be activated alphabetically. These triggers can call functions written in other languages. 

15. What kinds of Data Types does Postgresql support?

Various data types are supported, including:

  •  Arbitrary precision numbers
  •  rudimentary geometric shapes
  •  arrays
  • XML, etc.

Users can build and index their indexes.

15 Intermediate PostgreSQL Interview Questions

16. Is it possible to set up a PostgreSQL server cluster with shared storage?

They offer several different clustering tools that employ multiple clustering algorithms because no single type of clustering may meet all requirements. There are accessible open-source forks and proprietary tools like Greenplum Database, Citus Data, and others, and the open-source projects PostgresXC and Postgres-XL.

Additionally, filesystem-based clustering technologies for failover from Red Hat, Microsoft, Veritas, and Oracle are compatible with PostgreSQL.

17. What exactly are string constants?

Single quotes separate the characters in a string constant. This feature is utilized when inserting a character or providing a character to database objects. PostgreSQL permits using single quotes; however, they must be enclosed by a backslash in the C manner. This function is crucial for data parsing. 

18. What Different Postgresql Enhancements Are Made To The Straight Relational Data Model?

Postgre SQL offers several improvements over the basic relational data model, including inheritance, functions, extensibility, and support for multiple-choice arrays. Because it is object-oriented and refers to tables as classes, the jargon is unique.

19. How are Postgresql stats updated?

A call to explicitly "vacuum" is performed in PostgreSQL to update statistics. I hope you are aware of how to do this. If not, please inform us so we can assist you. Postgresql statistics are updated using a vacuum with the option Analyze. The syntax is VACUUM ANALYZE; 

20. What contrasts exist between Postgresql and NoSQL?

It is nonsensical to compare and make general statements about "NoSQL" Databases (Not Only SQL), which are a diverse variety of non-relational databases ranging from tiny embedded databases to enormous clustered (HA/Sarding) data processing platforms like Hadood & MongoDB. Choosing between relational and non-relational databases is not unusual because non-relational databases have been side by side with relational databases for 40 years.

The following factors should be considered by users when choosing a database

  • Features,
  • Functionalities,
  • Scalability
  • Reliability,
  • Implementing HA capabilities (Replication)
  • Community assistance is needed for their current application.

Additionally, using numerous databases for large projects is becoming the norm, and PostgreSQL is by no means an exception. 

21. What Has Changed in Postgre 9.1?

As always, we cannot predict what will be accepted and what won't because the project has rigorous quality requirements, and certain patches may not be accepted in time. Only what is in development, such as synchronous replication, JSON support, security labels, nearest-neighbor geographic searches, SQL/MED external data connections, column-level collations, and index-only access, can be revealed. However, by the time 9.1 is launched, this feature list will have significantly changed. 

22. Is Postgresql a Cloud-based Database?

Yes. PostgreSQL is portable and runs well in virtual containers like other open-source databases. Heroku, GoGrid, and Joyent are just a few businesses that offer PostgreSQL in cloud hosting settings. 

23. How Do Oracle/db2/ms SQL Server/Informix and Postgresql Compare?

Most experts believe our feature set is quite competitive with other top SQL RDBMSes. There are qualities that some of them undoubtedly possess that we do not, and the opposite is also true. Few benchmarks have been released, revealing that PostgreSQL is only 10–30% slower than proprietary competitors. However, the performance of their PostgreSQL systems has left many of our users who migrated from other database systems—primarily Oracle and Informix—completely delighted. 

24. What are Connector Libraries?

It consists of several connectors that may be downloaded and altered in any ProcessMaker instance. The connector public library is managed and updated constantly by the ProcessMaker. 

25. What is Full-Text Search? Does Postgresql offer support for it?

It is a methodology or approach for searching a single or group of digitally recorded documents in a full-text database. It is simple to distinguish it from searches that use metadata or pieces of the original texts represented in databases.

PostgreSQL is not as sophisticated as Elasticsearch or SOLR, but both are designed specifically for full-text search tools. Full-text search is only a feature in PostgreSQL, though it is good. 

26. What do you understand by inverted files in PostgreSQL?

In PostgreSQL, an inverted file is an index data structure used to map content to its location in a database file, within a document, or in sets of documents. It generally includes the distinct words found in a text and a list containing the occurrences of a word in the text. It is used in a data structure for document retrieval systems to provide a full-text search. 

27. What drawbacks does PostgreSQL have?

There is more than one company that owns Postgres. As a result, although fully functional and similar to other DBMS systems, it has had problems building a brand.

  • Compared to MySQL, PostgreSQL requires more work to make changes for speed enhancement because it prioritizes compatibility.
  • Though many open source applications may not support PostgreSQL, MySQL is.
  • It is slower than MySQL in terms of performance measures.

28. What is a Foreign Data Wrapper (FDW) in PostgreSQL, and how can it be used for data integration?

FDW allows accessing external data sources (other databases or file systems) as if they were PostgreSQL tables. It enables seamless data integration and querying between PostgreSQL and other data sources.

29. What are Materialized Views in PostgreSQL, and how do they differ from regular views?

Materialized Views store the query results physically in the database, allowing faster access and reducing query processing time. Regular views are virtual and do not store data directly; they are based on the underlying tables and retrieve data on-the-fly when queried.

30. What are Advisory Locks in PostgreSQL, and how can they be used for application-level locking?

Advisory Locks are lightweight locks that can be acquired programmatically by applications for synchronization purposes. Unlike standard locks, Advisory Locks do not conflict with regular table-level locks and can be used for application-specific coordination.

15 Advanced and PostgreSQL Interview Questions

31. What is a Foreign Data Wrapper (FDW) in PostgreSQL, and how can it be used for data integration?

A Foreign Data Wrapper (FDW) is a PostgreSQL feature that allows you to access data from external databases or file systems as if it were part of the PostgreSQL database. FDWs enable PostgreSQL to integrate with other databases like MySQL, Oracle, or even non-relational data sources such as CSV files. By using FDWs, you can execute SQL queries across different data sources within a single PostgreSQL query, providing seamless data integration. This capability is especially useful in heterogeneous environments where data resides in multiple systems.

32. What are Materialized Views in PostgreSQL, and how do they differ from regular views?

Materialized Views in PostgreSQL are database objects that store the result of a query physically, unlike regular views, which are virtual tables and don’t store data. Materialized Views are periodically refreshed to ensure the stored data is up-to-date. They are useful when you need to optimize complex queries that run frequently, as they reduce the need to re-execute the query every time. However, they require storage space and can become stale if not refreshed regularly, whereas regular views always provide real-time data.

33. What are Advisory Locks in PostgreSQL, and how can they be used for application-level locking?

Advisory Locks in PostgreSQL are a mechanism that allows you to manage application-level locks. Unlike traditional row-level locks, advisory locks are not tied to specific database objects like rows or tables. Instead, they are user-defined and can be used to control access to resources that are external to the database, such as files or network connections. Advisory locks are lightweight and can be acquired or released explicitly by the application, making them suitable for scenarios where you need to ensure that only one process accesses a resource at a time.

34. Explain the concept of JSONB in PostgreSQL and its benefits.

JSONB is a binary representation of JSON data in PostgreSQL. Unlike the plain JSON data type, which stores JSON as a text string, JSONB allows for more efficient processing, indexing, and querying of JSON data. With JSONB, PostgreSQL can store complex JSON structures and perform operations like indexing on individual elements, making it a powerful tool for handling semi-structured data. JSONB is particularly useful in scenarios where you need to combine the flexibility of NoSQL databases with the robustness of a relational database.

35. How does PostgreSQL handle concurrency with Multi-Version Concurrency Control (MVCC)?

PostgreSQL uses Multi-Version Concurrency Control (MVCC) to manage concurrent transactions efficiently. MVCC allows multiple transactions to access the database simultaneously without locking the data. Each transaction sees a consistent snapshot of the database at a particular point in time, and changes made by a transaction are invisible to others until the transaction is committed. This mechanism reduces the need for locking, improves performance, and ensures that transactions are isolated from each other, providing a consistent view of the data.

36. What is the significance of PostgreSQL’s WAL (Write-Ahead Logging)?

Write-Ahead Logging (WAL) is a critical feature in PostgreSQL that ensures data integrity and durability. WAL records all changes made to the database before they are actually applied to the data files. This log can be used to restore the database to a consistent state in the event of a crash or unexpected shutdown. WAL also plays a crucial role in replication, as the log can be shipped to standby servers to keep them synchronized with the primary database. This feature makes PostgreSQL highly reliable and robust in handling data.

37. How does PostgreSQL support full-text search, and what are its key features?

PostgreSQL provides robust full-text search capabilities, allowing you to search for specific words or phrases within text data. The key features include the ability to create indexes using tsvector and tsquery data types, support for ranking search results based on relevance, and the ability to use complex queries with logical operators. Full-text search in PostgreSQL is highly efficient, making it suitable for applications that require quick and accurate text search, such as document management systems or content-heavy websites.

38. What is the role of pg_stat_statements in PostgreSQL, and how can it be used for query optimization?

pg_stat_statements is an extension in PostgreSQL that tracks execution statistics for SQL statements. It provides detailed information about the queries executed, including execution time, number of calls, and frequency. This information can be used to identify slow or inefficient queries, helping database administrators and developers optimize the database's performance. By analyzing the statistics, you can pinpoint the queries that need optimization, whether through indexing, rewriting, or adjusting query plans.

39. How can you implement partitioning in PostgreSQL, and what are its advantages?

Partitioning in PostgreSQL involves dividing a large table into smaller, more manageable pieces called partitions. Each partition can be stored in a separate physical location, and queries can be optimized to access only the relevant partitions. PostgreSQL supports several partitioning methods, including range, list, and hash partitioning. The advantages of partitioning include improved query performance, easier data management, and reduced maintenance overhead. Partitioning is particularly beneficial for large datasets, where it can significantly reduce the time required for queries and maintenance tasks.

40. What are the different types of indexes in PostgreSQL, and when should each be used?

PostgreSQL supports several types of indexes, including B-tree, Hash, GIN (Generalized Inverted Index), GiST (Generalized Search Tree), and SP-GiST (Space-Partitioned Generalized Search Tree). B-tree is the most commonly used index and is suitable for general-purpose indexing. Hash indexes are faster for equality comparisons but are less versatile. GIN and GiST are used for full-text search and indexing complex data types like JSONB or geometric data. SP-GiST is designed for partitioned data. Choosing the right index depends on the specific use case and the type of queries you expect to run.

41. How do you perform replication in PostgreSQL, and what are the available methods?

Replication in PostgreSQL involves copying data from one database (the primary) to another (the replica) to ensure high availability and fault tolerance. PostgreSQL offers several replication methods, including streaming replication, logical replication, and file-based log shipping. Streaming replication continuously streams WAL files from the primary to the replica in real-time. Logical replication allows you to replicate specific tables or databases and supports bidirectional replication. File-based log shipping involves periodically copying and applying WAL files to the replica. Each method has its use cases, depending on the required level of consistency and the network environment.

42. What is a Hot Standby in PostgreSQL, and how does it work?

Hot Standby in PostgreSQL is a feature that allows you to run read-only queries on a replica database while it is replicating data from the primary database. This setup provides high availability by allowing the replica to be used for query processing, thus offloading some of the workloads from the primary database. Hot Standby works in conjunction with streaming replication, where the replica continuously receives WAL records from the primary. In the event of a failure on the primary, the replica can be promoted to take over as the new primary, minimizing downtime.

43. Explain the concept of VACUUM in PostgreSQL and why it is necessary.

VACUUM in PostgreSQL is a maintenance operation that cleans up dead tuples left behind after DELETE and UPDATE operations. Since PostgreSQL uses MVCC to handle concurrency, old versions of rows are retained until they are no longer needed. VACUUM reclaims the space occupied by these dead tuples, making it available for new data. It also updates the visibility map and helps to prevent transaction ID wraparound issues. Regularly running VACUUM is essential to maintain database performance and ensure efficient use of storage.

44. How does PostgreSQL handle transactional integrity, and what are the ACID properties?

PostgreSQL ensures transactional integrity through the ACID (Atomicity, Consistency, Isolation, Durability) properties. Atomicity guarantees that all operations within a transaction are completed successfully or none are applied. Consistency ensures that transactions bring the database from one valid state to another, maintaining data integrity. Isolation means that transactions are executed independently, preventing interference from other transactions. Durability ensures that once a transaction is committed, its changes are permanently recorded, even in the event of a crash. PostgreSQL’s robust implementation of ACID properties makes it a reliable choice for critical applications.

45. What are the benefits and challenges of using PostgreSQL in a cloud environment?

PostgreSQL offers several benefits in a cloud environment, including scalability, flexibility, and support for a wide range of data types and extensions. Cloud platforms often provide managed PostgreSQL services, simplifying database management and reducing administrative overhead. However, challenges include managing latency, ensuring data security, and optimizing performance for distributed workloads. Additionally, cost management can be complex, as cloud resources can become expensive if not carefully monitored. Despite these challenges, PostgreSQL's robust features and cloud-friendly nature make it a popular choice for modern applications.

PostgreSQL MCQs

1. What is the default port number for PostgreSQL?

A) 3306
B) 1521
C) 5432
D) 1433
Answer: C) 5432

2. Which PostgreSQL command is used to create a new database?

A) CREATE TABLE
B) CREATE DATABASE
C) CREATE SCHEMA
D) CREATE USER
Answer: B) CREATE DATABASE

3. What does the VACUUM command do in PostgreSQL?

A) Deletes the database
B) Optimizes database performance by cleaning up unused space
C) Backs up the database
D) Creates a new index
Answer: B) Optimizes database performance by cleaning up unused space

4. Which PostgreSQL feature allows you to execute SQL commands from a file?

A) psql
B) pgAdmin
C) pg_dump
D) pg_restore
Answer: A) psql

5. How do you list all the tables in a PostgreSQL database?

A) SELECT * FROM tables;
B) SHOW TABLES;
C) \dt
D) LIST TABLES;
 Answer: C) \dt

Frequently Asked Questions

What is the main purpose of PostgreSQL?

The main purpose of PostgreSQL is to store, manage, and retrieve structured data for various applications, providing a reliable and powerful open-source database solution.

What is the latest version of PostgreSQL?

The latest version of PostgreSQL is 15. There are so many features they have introduced in this version. We will have a more secure permission model in this version. They have also added a MERGE operation in it and many other features.

Why is PostgreSQL the most loved database?

PostgreSQL is highly regarded and loved for its advanced features, extensibility, reliability, and adherence to SQL standards. This makes it more suitable for a wide range of applications. Additionally, its open-source nature fosters a strong community and continuous improvement.

Conclusion

In this article, we have covered a comprehensive range of PostgreSQL interview questions, spanning from fundamental concepts to advanced topics. Whether you're preparing for a role as a fresher or aiming for a position requiring advanced expertise, these questions and answers should provide valuable insights and preparation. We hope you find this resource helpful and wish you the best in your PostgreSQL journey.

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