PostgreSQL Interview Questions

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  • User AvatarAshiwini
  • 30 Jan, 2025
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PostgreSQL Interview Questions

  1. What is PostgreSQL?

    PostgreSQL is a lightweight, free, and open-source relational database management system. PostgreSQL is used widely across regions and companies and can be used in most popular operating systems.

  2. What are the benefits of PostgreSQL?

    PostgreSQL excels among other SQL databases for several reasons, including:
    1.Robustness that makes it suitable for all kinds of applications
    2.Free and open-source
    3.Security and reliability
    4.Wide variety of data types
    5.A big community of users worldwide.

  3. What are the main applications of PostgreSQL?

    PostgreSQL allows you to:
    1.Create, delete, and update tables in a database,
    2.Access, manipulate, and modify data in a table,
    3.Retrieve and summarize the necessary information from a table or several tables,
    4.Add or remove certain rows or columns from a table

  4. What are CRUD operations in PostgreSQL?

    CRUD (Create, Read, Update, Delete) operations are the basic operations in any SQL database system, including PostgreSQL. CRUD operations are frequently used in database design and management.

  5. What is a constraint in PostgreSQL?

    A set of conditions defining the type of data that can be input into each column of a table. Constraints are used to ensure data integrity in a table and prevent undesired actions.

  6. What is a join in PostgreSQL?

    Joins are used to combine and retrieve records from two or multiple tables. PostgreSQL uses standard SQL joins to perform these kinds of operations.

  7. How can you create a new database in PostgreSQL?

    PostgreSQL uses the standard CREATE DATABASE command to create new databases. But the devil is in the details. There is so much to consider when creating a database, that’s why we have prepared our Creating PostgreSQL Databases Course to get you covered.

  8. Can you explain what is a primary key in PostgreSQL?

    A primary key is used to identify a row uniquely in a table. Primary keys may be made of one column or multiple columns. A primary key can be classified as a type of constraint.

  9. What is a schema in PostgreSQL?

    A database schema contains the logical and visual configuration of the entire relational database. In PostgreSQL, it includes the tables, along with the data types, views, indexes, sequences, constraints, and functions.

  10. What is a database in PostgreSQL?

    As in other SQL dialects, the database is a structured storage space where the data is kept in many tables and organized so that the necessary information can be easily fetched, manipulated, and summarized.

  11. How can you select the five first rows in a table called ‘customers’ in PostgreSQL?

    You can retrieve that data using the following query:
    SELECT * FROM customers LIMIT 5;

  12. What is pgAdmin in PostgreSQL?

    pgAdmin is a handy utility that comes with the PostgreSQL installation, and it lets you do regular database-related tasks through a nice graphical interface.

  13.  Can you run PostgreSQL on the cloud?

    Yes, PostgreSQL is compatible and can be run on most popular cloud providers, including AWS, Azure, and Google Cloud.

  14. How can you add new values to a certain table?

    PostgreSQL uses the standard INSERT INTO statement to add data to your SQL table.

  15. How can you delete a database in PostgreSQL?

    To delete a database in PostgreSQL, use the DROP DATABASE command.

  16. What is the difference between a foreign key and a primary key in PostgreSQL?

    A foreign key provides shared keys between two or more tables, whereas a primary key allows only unique and strictly non-null values. Both are considered types of constraints.

  17. Is PostgreSQL compatible with Python?

    Yes, there are many packages available that allow you to use PostgreSQL through Python. Psycopg is one of the most popular Python libraries for PostgreSQL. Curious about how to use PostgreSQL through Python? Read our separate article Using PostgreSQL in Python Tutorial: Create, Connect, and Manage Databases.

  18. What is the latest version of PostgreSQL?

    As of January 2024, the latest version is PostgreSQL 16.

  19. What are the main constraints in PostgreSQL?

    PostgreSQL providers for the following constraints:

    Check Constraints
    Not-Null Constraints
    Unique Constraints
    Primary Keys
    Foreign Keys
    Exclusion Constraints

  20. What is PL/Python in PostgreSQL?

    PostgreSQL provides support to a procedural language known as PL/Python. This allows you to write SQL functions and procedures using Python.

  21. What is an index in PostgreSQL?

    An index is a special data structure related to a table and used for storing its important parts and enabling faster data search and retrieval. This is achieved by creating a sorted data structure that allows PostgreSQL to locate rows more quickly compared to a full table scan. Indexes are especially efficient for large databases, where they significantly enhance query performance.

  22. What is partitioning in PostgreSQL?

    It’s the process of splitting a large table into smaller pieces. It can be done through several methods, including range partitioning, list partitioning, and hash partitioning.

  23. What is Multi-version Concurrency Control in PostgreSQL?

    Multi-version Concurrency Control or MVCC is an advanced technique in PostgreSQL. It enhances database performance in multi-user scenarios. This means that while querying a database each transaction sees a snapshot of data (a database version) as it was some time ago, regardless of the current state of the underlying data. This protects the transaction from viewing inconsistent data that could be caused by (other) concurrent transaction updates on the same data rows.

  24. What are the main operators in PostgreSQL?

    The main types of operators available in PostgreSQL are:Arithmetic operators
    Logical operators
    Comparison operators
    Bitwise operators

  25. What is Write-Ahead Logging in PostgreSQL?

    Write-ahead logging is a technique used to ensure the data integrity of PostgreSQL databases. Write-ahead logging ensures that any changes and actions in the database are logged in a transaction log before the updating or modification of the database. In case of a database crash, this helps in providing the log of the database changes.

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

    While PostgreSQL provides unlimited database size, there is a maximum size for tables, which is set to 32 TB.

  27. How can you make a backup of a database in PostgreSQL?

    Making a backup of your database in PostgreSQL is fairly simple. There are various methods to perform a backup in PostgreSQL, including:
    SQL dump
    File system-level backup
    On-line backup

  28. What is the pg_dump method used for?

    The pg_dump method allows you to create a text file with a set of SQL commands that, when run in a PostgreSQL server, will recreate the database in the same state as it was at the moment of the dump.

  29. What types of joins are available in PostgreSQL?

    In PostgreSQL, the main joins are:
    INNER JOIN: Returns records that have matching values in both tables
    LEFT JOIN: Returns all records from the left table, and the matched records from the right table
    RIGHT JOIN: Returns all records from the right table, and the matched records from the left table
    FULL JOIN: Returns all records when there is a match in either left or right table

  30. How can you delete a table, as well as any other object associated with it, such as views, triggers, functions, and stored procedures?

    To delete a table in PostgreSQL, use the DROP TABLE command, followed by the name of the table. To ensure that any other object is associated with it, you will need to add the CASCADE command.