Introduction to PostgreSQL Interview Questions and Answers

PostgreSQL is an object-relational database management systems (ORDBMS). It is a powerful, open-source object-relational database system. PostgreSQL is not controlled by any corporation or other private entity and the source code is available free of charge. PostgreSQL runs on all major operating systems, including Linux, UNIX, and Windows. It supports text, images, sounds and video, and includes programming interfaces for C/C++, Java, Perl, Python, Ruby and Open Database Connectivity.

Installation

Follow these steps to install PostgreSQL on Windows system:

Pick the most relevant version on PostgreSQL from EnterpriseDB.
Run the downloaded software as administrator. Select the location where you want to install it.
Next step of installation is selecting the directory where data should be stored. By default, it is stored under the “data” directory.
It will prompt to enter a password to make data stored more secure.
Next step is to set a default port.
On completion of installation, a message is displayed.

Features of PostgreSQL

Language support: PostgreSQL supports four standard procedural languages PL/pgSQL, PL/Tcl, PL/Perl and PL/Python.
Indexes: PostgreSQL supports B+ tree, hash, generalized search trees and generalized inverted indexes. Users can also create their own customized indexes.
Views: views that create virtual tables is supported by PostgreSQL.
Rules: rules allow a hierarchy of incoming query to be re-written, are supported by PostgreSQL.
Inheritance: in PostgreSQL, a table can be set to inherit their characteristics from a “parent” table.
User-defined functions: it supports the creation of almost all new objects inside the database like Casts, conversions, dataTypes, domains, functions including aggregate functions, indexes including custom indexes for custom types operator.

Now, if you are looking for a job which is related to PostgreSQL then you need to prepare for the PostgreSQL Interview Questions. It is true that every interview is different as per the different job profiles but still to clear the interview you need to have a good and clear knowledge of PostgreSQL processes. Here, we have prepared the important PostgreSQL Interview Question and answers which will help you get success in your interview.

Below are the 12 important PostgreSQL Interview Questions and answers that are frequently asked in an interview. These questions are divided into two parts are as follows:

Part 1 – PostgreSQL Interview Questions (Basic)

This first part covers basic PostgreSQL Interview Questions and Answers.

Q1. What are the main features of PostgreSQL?

Answer:
Following are some of the features of PostgreSQL

Object-relational database.
Support and extensibility for SQL.
Flexible API and database validation.
MVCC and procedural languages,
WAL and Client Server.

Q2. What is Cube Root Operator (||/) in PostgreSQL?

Answer:
Returns Cube Root of a number
e.g. Select ||/ 16 “Cube Root of 16”

Q3. Provide a brief explanation of the functions in PostgreSQL?

Answer:
Functions are an important part because they help in executing the code on the server. Some of the languages to program functions are PL/pgSQL, a native language of PostgreSQL, and other scripting languages like Perl, Python, PHP etc. statistical language named PL/R can also be used to increase the efficiency of the functions.

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Let us move to the next PostgreSQL Interview Questions.

Q4. Can you explain pgadmin?

Answer:
Pgadmin is a feature that is known to form a graphical front-end administration tool. This feature is available under free software released under Artistic License. Pgadmin iii is the new database administration tool released under artistic license.

Q5. What is Multi-version control?

Answer:
Multi-version concurrency control or MVCC is used to avoid unnecessary locking of the database. This removes the time lag for the user to log into his database. This feature or time lag occurs when someone else is accessing the content. All transactions are kept as a record.

Q6. What will be new characteristics of PostgreSQL 9.1?

Answer:
During the process of updating the project, one can never be certain that features will go in and which ones won’t make the cut. The project has precise and stringent standards for quality and some patches may or may not match them before the set deadline. Currently, the 9.1 version is working on some important features which include JSON support, synchronous replication, nearest-neighbor geographic searches, collation at the column level, SQL/MED external data connections, security labels as well as index-only access. However, this list has a high chance of changing completely by the time Postgre 9.1 is released.

Part 2 – PostgreSQL Interview Questions (Advanced)

Let us now have a look at the advanced PostgreSQL Interview Questions.

Q7. What is command enable-debug?

Answer:
The command enable-debug is used to enable the compilation of all the applications and libraries. The execution of this procedure usually impedes the system, but it also amplifies the binary file size. Debugging symbols which are present generally assist the developers in spotting the bugs and other problems which may arise associated with their script.

Q8. What are the indices of PostgreSQL?

Answer:
These are inbuilt functions or methods like GIST Indices, hash table and B-tree which can be used by the user to scan the index in a backward manner. Users can also define their indices of PostgreSQL.

Q9. What is the option in PostgreSQL to check rows that are affected in a previous part of the transaction?

Answer:
The SQL standard is defined by four levels of transaction isolation basically regarding three phenomena. The three phenomenon must be prevented between concurrent transactions. The unwanted phenomenon is

Phantom read: a transaction that re-executes a query, returning a set of rows that satisfy a search condition and then finds that the set of rows that have been satisfying the condition has changed due to other recently committed transaction.
Non-repeatable read: a transaction that re-reads the data that it has previously read then finds that data has already been modified by another transaction.
Dirty reads: a transaction when reads data that is written by a concurrent uncommitted transaction is the dirty read.

Let us move to the next PostgreSQL Interview Questions.

Q10. What is A Ctid?

Answer:
CTIDs is a field, which exists in every PostgreSQL table and is known to identify specific physical rows according to their block and offset positions within a particular table. They are used by index entries to point to physical rows. It is unique for each record in the table and easily denotes the location of a tuple. A logical row’s CTID changes when it is updated, so the CTID cannot be used as a long-term row identifier. However, it is sometimes useful to identify a row within a transaction when no competing update is expected.

Q11. What are the tokens?

Answer:
Token are the building blocks of any source code. They are known to comprise many of the special character symbols. These can be regarded as constant, quoted identifiers, other identifiers, and keywords. Tokens which are keywords consist of pre-defined SQL commands and meanings. Identifiers are used to represent variable names like columns, tables etc.

Q12. What is the purpose of Array_To_String in PostgreSQL?

Answer:
The Array_To_String function concatenates array elements using a provided delimiter.