Prashant Sharma — Updated On July 28th, 2022
Beginner Database Interview Questions Interviews SQL

This article was published as a part of the Data Science Blogathon.

Introduction to PostgreSQL

PostgreSQL is one of the most often used languages for Object-Relational Database Management Systems. It is put to use mostly for huge web applications. It is an object-oriented, relational, open-source database system. It is incredibly potent and allows users to extend any system without difficulty. It extends the SQL language and employs multiple capabilities to safely scale and store complex data workloads.

Features of PostgreSQL

  • Language support: PostgreSQL supports four standard procedural languages, including PL/pgSQL, PL/Tcl, PL/Perl, and PL/Python.
  • Indexes: PostgreSQL indexes support B+ tree, hash, generalized search trees, and generalized inverted indexes. Individuals can also design their own personalized indexes.
  • Views: Views that generate virtual tables are supported by PostgreSQL.
  • Rules: PostgreSQL supports rules, which allow the rewriting of a query’s hierarchical structure.
  • Inheritance: In PostgreSQL, a table may be configured to inherit attributes from a “parent” table via inheritance.
  • User-defined functions: It facilitates the construction of practically all new database objects, including Casts, conversions, dataTypes, domains, functions, aggregate functions, and indexes, including custom indexes for custom kinds operator.

Interview Questions for PostgreSQL

1. What are the core advantages of PostgreSQL?

The following are some of PostgreSQL’s features:

  • Relational object database.
  • SQL support and extensibility
  • API and database validation flexibility.
  • MVCC and procedural languages,
  • WAL and Client-Server.

2. List the various data types supported by PostgreSQL.

The following are some of the new data types added to PostgreSQL:

  • UUID
  • Numeric types
  • Boolean
  • Character types
  • Temporal types
  • Geometric primitives
  • Arbitrary precision numeric
  • XML
  • Arrays, etc.

3. What are PostgreSQL’s tokens?

In PostgreSQL, tokens serve as the building elements of source code. They are comprised of a variety of special character symbols. Tokens are keywords mainly made up of predefined SQL commands and meanings. Commands comprise a sequence of tokens separated by a semicolon (‘;’). These may comprise of a constant, a quoted identifier, additional identifiers, a keyword, or a constant. Typically, Whitespace separates tokens.

4. What are the PostgreSQL Indices?

Indexes are a special PostgreSQL tool used to improve data retrieval from databases. A database index is similar to a book index. An index provides access to all the values in the indexed columns.PostgreSQL indexes let the database server locate and retrieve specific rows contained within a particular framework. B-tree, hash, GiST, SP-GiST, GIN, and BRIN are other examples. In PostgreSQL, users are indeed free to create their own indices. However, indices increase the complexity of data processing operations and are rarely employed.

5. How do I set up a PostgreSQL database?

There are two ways to generate databases. The CREATE DATABASE SQL command comes first.

Using the following syntax, we may build the database:-CREATE DATABASE ;

The second approach makes use of the createdb command.

We could establish the database with the following syntax:- createdb [option…] [description].

Depending on the use scenario, the createDB command may take many arguments.

6. How you can create a table in PostgreSQL?

You may create a new table by defining the table’s name, along with the names and types of each column:
column1 datatype(length) column_contraint,
column2 datatype(length) column_contraint,
columnn datatype(length) column_contraint,

7. Contrast ‘PostgreSQL’ to ‘MongoDB’

PostgreSQL is a SQL database in which data is stored in rows and columns of tables. It supports notions like entity-relationship integrity and JOINS. The PostgreSQL querying language is SQL. PostgreSQL supports vertical scaling. This necessitates the usage of large servers for data storage. This results in the need for downtime to update. It performs better if your application requires relational databases or if you need to carry out complex queries that exceed the capabilities of SQL.In contrast, MongoDB is a NoSQL database. There is no necessity for a schema, therefore unstructured data can be stored. Data is saved in BSON documents, the structure of which may be reformed by the user. MongoDB queries are written in JavaScript. As a result of its adaptability for horizontal scaling, extra servers may be added as needed with low to no downtime. A use case that necessitates a highly scalable, distributed database that holds unstructured data is suited for this technology.

8. What is PostgreSQL’s Multi-Version concurrency control?

PostgreSQL uses MVCC, also regarded as Multi-version concurrency control, to implement transactions. It is used to prevent unintended database lockout in the system. Each transaction that queries a database sees a different version of the database. This prevents the display of inconsistent data and provides transaction isolation for each database session. MVCC locks for data reading do not interfere with locks acquired for writing data.

9. What exactly is pgAdmin?

pgAdmin is a Web-based GUI utility for interacting with Postgres database sessions. It is applicable to both local and distant servers. Its most recent release, pgAdmin4, is distributed under the PostgreSQL License. pgAdmin4 creation required a complete rebuild of the original pgAdmin program. This version was made with a mix of Javascript/jQuery and Python. pgAdmin can now be used as a desktop runtime or as a web application server, depending on your needs.

10. How is the database deleted in PostgreSQL?

Using the syntax, databases may be removed in PostgreSQL.DROP DATABASE [IF EXISTS] ;

Please note that only inactive databases can be discarded.

11. What does a schema consist of?

Schemas are elements of databases, including tables. They include data types, functions, and operators, among other named object types. The object names are compatible across schemas; unlike databases, schemas are divided more freely. This indicates that a user can access objects in any of the schemas in the database they are linked to until they are granted the appropriate permissions. Schemas are incredibly beneficial when several users must access a single database without interfering with one another. It facilitates the organization of database items into logical categories for better management. To prevent name-based conflicts, third-party applications could be placed in distinct schemas.

12. What are the most significant differences between SQL and PostgreSQL?

PostgreSQL is a sophisticated SQL variant. PostgreSQL views cannot be updated.PostgreSQL does not support calculated columns. However, it does provide functional indexes. In PostgreSQL, replication takes the form of reports. PostgreSQL provides actions that are dynamic.

The PostgreSQL server provides several levels of encryption and flexibility to improve data security from disclosure in an insecure network scenario. Meanwhile, the SQL server is designed to provide a safe database platform. To that end, it includes several capabilities that can encrypt data, decrease authorization, and protect data from unethical acts.

13. Explain Write-Ahead Logging in detail.

Write-ahead logging (WAL) is vital to Postgres’ durability and data consistency. All modifications are initially captured to this append-only log, then to the data files on disk. Using write-ahead logging, you can protect your data against corruption. As a result of this method, a complete record of all operations and alterations is maintained. It’s well-known that backing up database changes before implementing or updating them improves the stability of certain databases. A backup log is kept here in case the database fails. When Postgres enforces write operations, it creates WAL (e.g., INSERT, UPDATE, etc.). In situations when WAL creation exceeds the capability of WAL archival off-disk or where a high database load reduces archiver performance, WAL capacity is limited.

14. What is the definition of a non-clustered index?

A non-clustered index in PostgreSQL is a simple index used to quickly retrieve data with no assurance of uniqueness. It includes references to other places where data is kept. This is known as a secondary index too. You can have several indices of this category as you want on a given table. Non-clustered indexes are analogous to a document’s “Table of Contents.” We check the page number first, then the page numbers after that to view the entire content. It keeps a pointer to corresponding heap data to get the whole data based on an index. It’s exactly similar to knowing the page number and then going to that page to retrieve the actual content of the page.

15. How does PostgreSQL provide security?

PostgreSQL employs two tiers of security.

  1. Network-level security- Utilization of Unix Domain sockets, TCP/IP sockets, and firewalls for network-level security.

  2. Transport-level security- Transport-level security employs SSL/TLS to ensure the safe database communication

  3. Database-level security- Roles and permissions, row-level security (RLS), and auditing are all characteristics of database-level security.


In this article, we have seen important PostgreSQL questions. We got a good understanding of different PostgreSQL terminologies. Below are some major takeaways from the above article:

1. We have seen PostgreSQL’s tokens and what are the benefits of using PostgreSQL.

2. We learned about How to set up a PostgreSQL database?

3. We got an understanding of how we can create a table in PostgreSQL?

And much more.

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About the Author

Prashant Sharma

Currently, I Am pursuing my Bachelors of Technology( B.Tech) from Vellore Institute of Technology. I am very enthusiastic about programming and its real applications including software development, machine learning and data science.

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