Register Login
Python Photoshop SAP Java PHP Android C++ Hadoop Oracle Interview Questions Articles Other

PostgreSQL Interview Questions and Answers

Updated Apr 28, 2025

What is PostgreSQL?

PostgreSQL is an open source object-relational database management system. It runs on multiple operating systems and supports different programming languages like C, C++, Python, Ruby, Perl, etc.

It supports JSON for non-relational queries and SQL for relational queries. It provides enhanced support for performance optimization and multiple data types.

What are the advantages and disadvantages of PostgreSQL?

The advantages of PostgreSQL are:

  • It runs on multiple operating systems like Windows, Linux, and Mac.
  • It supports different programming languages like C, C++, Python, Ruby, Perl, etc.
  • It is relatively easy for beginners to learn.
  • It can run many web applications and dynamic websites under the LAMP stack.
  • It can be used for location-based services as it supports geographic objects.

The disadvantages of PostgreSQL are:

  • Many open source applications do not support it.
  • It can be slower than MySQL in certain use cases.
  • It does not support the entire ANSI SQL 92 standard, but it supports most of it.
  • Speed upgrades can take time in some cases.
  • Many hosting platforms do not support it.

What PostgreSQL command-line utility backs up PostgreSQL databases?

In PostgreSQL, the pg_dump utility is used to back up PostgreSQL databases, including their schema and data.

What are PostgreSQL databases?

A PostgreSQL database has an object-relational structure and the following properties:

  • Foreign key referential integrity
  • Table inheritance
  • User-defined data types
  • Asynchronous replication
  • Enhanced locking systems
  • MVCC (Multi-Version Concurrency Control)
  • Custom functions in languages like Java and C
  • Custom plugins can be added to extend functionality.

What are the various features of PostgreSQL?

The features of PostgreSQL are:

  • It runs on multiple operating systems like Windows, Linux, and Mac.
  • It supports different programming languages like C, C++, Python, Ruby, Perl, etc.
  • It supports geographical information systems with geographic objects.
  • It uses advanced locking mechanisms.
  • It supports MVCC (Multi-Version Concurrency Control).
  • It has enhanced server-side programming functionality.
  • It supports client-server network architecture.
  • It is fully ACID compliant.

How to alter a column datatype in PostgreSQL?

To change the data type of a column in PostgreSQL:

  • After the ALTER TABLE command, specify the name of the table.
  • After the ALTER COLUMN command, provide the column name.
  • Then use the SET DATA TYPE command to specify the new data type.

Syntax:

ALTER TABLE table_name
ALTER COLUMN column_name [SET DATA] TYPE new_data_type;

How to create a table in PostgreSQL?

To create a table in PostgreSQL:

  • After the CREATE TABLE command, provide the table name.
  • Then provide the column name and data type, along with constraints like NOT NULL.
  • Define any table-level constraints to set rules for the table.

Syntax:

CREATE TABLE table_name (
column_name TYPE column_constraint,
table_constraint table_constraint
);

How to delete a table in PostgreSQL?

To delete a table in PostgreSQL, use the following command:

DROP TABLE table_name;

This will remove the table and all dependent objects such as indexes and constraints.

How to add a column in PostgreSQL?

To add a column to a table in PostgreSQL:

  • After the ALTER TABLE command, specify the table name.
  • Use the ADD COLUMN command followed by the new column name and data type.

Syntax:

ALTER TABLE table_name
ADD COLUMN new_column_name data_type;

How to reset serial in PostgreSQL?

For columns with data type serial, connected to a sequence, you can reset the sequence using the following command:

setval(, );

What is the maximum size of a table in PostgreSQL?

The maximum size of a table in PostgreSQL is typically 32 TB, depending on your hardware and available disk space.

How to insert a date in PostgreSQL?

Use the NOW() function to get the current date and time. The syntax is:

SELECT NOW();

Alternatively, use the CURRENT_DATE function:

SELECT CURRENT_DATE;

How to concatenate two strings in PostgreSQL?

You can concatenate two strings using the CONCAT() function:

CONCAT(string1, string2);

Alternatively, use the || operator:

'string1' || 'string2' AS result_string;

What is the difference between PostgreSQL and MySQL?

Key differences between PostgreSQL and MySQL:

PostgreSQL MySQL
Object-relational database management system. Relational database management system.
Highly extensible. Less extensible than PostgreSQL.
Supports Data Domain Objects. Does not support Data Domain Objects.
Fully ACID compliant. ACID compliant with InnoDB and NDB clusters.
Supports MVCC for high concurrency. Supports MVCC in InnoDB.
Supports materialized views and temporary tables. Only supports temporary tables.

How do you create an index in PostgreSQL?

To create an index in PostgreSQL, the following syntax is used:

CREATE INDEX index_name ON table_name (column_name);

Where index_name is the name of the index, table_name is the name of the table, and column_name is the column to be indexed.

What is the difference between a primary key and a unique key in PostgreSQL?

Primary Key: A primary key is a column (or a set of columns) that uniquely identifies each row in a table. It cannot contain NULL values and must have a unique value for each row.

Unique Key: A unique key also ensures that the values in a column are unique, but it allows NULL values.

Recommended Posts:
×