PostgreSQL is one of the top databases in the world now. When it comes to open-source databases, it has occupied the number two position. So, along with its popularity, the demand for trained PostgreSQL professionals is also growing. Being one of the top training institutions providing quality PostgreSQL training in India, we intend to help the PostgreSQL job aspirants with the most frequently asked questions in the interviews.   

PostgreSQL Interview Questions and Answers

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

Ans. It is called table partitioning.

2. What is a partitioned table in PostgreSQL?

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

3. What purpose does pgadmin in PostgreSQL serve?

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

4. How can you avoid unnecessary locking of a database?

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

5. What is PL/Python? 

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

6. Which are the methods PostgreSQL provides to create a new database?

Ans. PostgreSQL provides the following methods to create a new database:

  • Using CREATE DATABASE, an SQL command
  • Using createdb a command-line executable

7. How do you delete the database in PostgreSQL?

Ans. 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

8. What does a schema contain? 

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

9. What are the different operators in PostgreSQL?

Ans. The PostgreSQL operators include - Arithmetic operators, Comparison operators, Logical operators, and Bitwise operators.

10. What are database callback functions called? What is their purpose?

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

11. What for indexes used?

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

12. What does a Cluster index do? 

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

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

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

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

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

15. What is the disadvantage with the DROP TABLE command in deleting complete data from an existing table?

Ans. 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 delete complete data from an existing table?

Ans. 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?

Ans. 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?

Ans. 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?

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

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

Ans. 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 whereas 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 the code what it is doing.

PostgreSQL supports dynamic actions whereas the SQL doesn’t support them.

21. How is security ensured in PostgreSQL?

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

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

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

23. What are the advantages of PostgreSQL?

Ans. 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. What does Write Ahead Logging do?

Ans. 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 data administration tools supported by PostgreSQL?

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

26. How can you store the binary data in PostgreSQL?

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

27. What is a non-clustered index?

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

28. What is the purpose of table space in PostgreSQL?

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

29. Are there any disadvantages with  PostgreSQL?

Ans. 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 represent in a SQL Statement?

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