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Updated by Arctype SQL Client on Apr 08, 2021
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12 PostgreSQL Interview Questions

If you’re interviewing for a position in which you’ll have to work with a database; there are some fundamental things that you should know. We have prepared some important PostgreSQL interview questions and answers which will help you succeed in your interview. Add questions you find difficult!

Source: https://arctype.com/blog/postgres-interview-questions/

1

What are the languages which PostgreSQL supports?

It supports a language of its own, PL/pgSQL and it supports internal procedural languages - Python, Perl, and Tcl.

2

What are the main features of PostgreSQL?

3

What is a non-clustered index?

A non-clustered index is a type of index where the order of the rows does not match the order of the actual data.

4

How can you store binary data in PostgreSQL?

PostgreSQL provides two distinct methods for storing binary data:

  • The first is by storing the binary data in a table using the data type bytea.
  • The second method is by using the Large Object feature, which stores the binary data in a separate table in a special format and refers to that table by storing a value of type oid in your table.

The bytea data type is not well suited for storing very large amounts of data, while the Large Object method for storing binary data is better suited for storing very large values.

5

Explain functions in PostgreSQL

Functions in PostgreSQL are also known as stored procedures. They are used to store commands, declarations, assignments, etc. This makes it easy to perform operations that would generally take thousands of lines of code to write.

PostgreSQL functions can be created in several languages such as SQL, PL/pgSQL, C, Python, etc.

6

How can we change the column data type in SQL?

Column data types in PostgreSQL are changed using the ALTER TABLE statement combined with the ALTER COLUMN statement.

ALTER TABLE table_name ALTER COLUMN column_name SET DATA TYPE new_data_type

7

What is a CTID?

This is a field that exists in every PostgreSQL table. It is a hidden and unique record for each table in PostgreSQL that easily denotes the location of a tuple and is known to identify certain physical rows according to their block and offset positions within a particular table. A logical row’s ctid changes when it is updated, so the ctid cannot be used as a long term identifier.

8

What is multi-version concurrency control in PostgreSQL?

It is a method commonly used to provide concurrent access to the database, and in programming languages to implement transactional memory. It avoids unnecessary locking of the database - removing the time lag for the user to log into the database.

9

What are tokens?

Tokens are the building blocks of any line of source code. A token can be a keyword, an identifier, a quoted identifier, a constant, etc. Tokens which are keywords consist of predefined SQL commands, while identifiers are used to represent variable names like columns and tables.

10

Explain how to enable debugging in PostgresSQL

This command is used for enabling the compilation of all libraries and applications. This process slows down the system and at the same time increases the binary file size. It can be turned on by installing the pldbgapi extension and running the command:
CREATE EXTENSION pldbgapi