PostgreSQL Interview Questions

Postgresql Interview Questions

Postgresql is a widely used system for Object-Relational Database Management that is mainly used for large web applications. Every year there are some vacancies, in big companies like Oracle, SQLite, Amazon web services and such others, to fill up in this field. People with technical expertise in the computer can easily crack the interview.

Here, we have listed few important and expected questions that may come up in your interview. With a little bit of practice and hard work and thoroughness, the questions can be understood. Going through the questions, you may find some questions that come up almost in every interview.

These predictable questions and answers will help you get through the interview without breaking a sweat.

Here are few Postgresql Interview questions with their answers:

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Postgresql Interview Questions

 Anywhere, 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.
 MVCC or better known as Multi-version concurrency control is used to avoid unwanted locking of the database. The time lag for the user is removed so that one can easily log into his database. All the transactions are well- kept as a record. The time lag occurs when someone else is on the content.
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 the transactions are kept as a record.
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 for spotting the bugs and other problems which may arise associated with their script. 
These are inbuilt functions or methods like GIST Indices, hash table and B-tree (Binary tree) which can be used by the user to scan the index in a backward manner. Users can also define their indices of PostgreSQL.
 Following are some of the features of Postgresql :
  1. Object-relational database
  2. Support and Extensibility for SQL
  3. flexible API and Database validation
  4. MVCC and Procedural languages
  5. WAL and Client server

The expression ‘NoSQL’ encompasses a wide collection of implementations which are part of the non-relational database. This includes tiny embedded databases such as TokyoCabinet, massive bunched data processing platforms such as Hadoop and everything in between. In short, it’s practically impossible to comment on the range comprised by NoSQL as a typical class.

Choosing between the non-relational and relational databases is also quite commonly debated as both have existed alongside each other for over forty years. In fact, users should opt for the features, community support and implementation of the database according to their current application needs. Additionally, use of multiple various databases for sizeable projects is becoming more of a norm than a trend. Moreover, the users of PostgreSQL are no exception.

There are the number of data administration tools, and they are
  • Phppgadmin
  • Psql
  • Pgadmin

Out of these, phppgadmin is the most popular one. Most of these tools are front-end administration tools and web-based interfaces.

 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.
 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 phenomena are:
  • 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 another recently-committed transaction.
  • Non-repeatable read: A transaction that re-reads the data that it has previously read and then finds that data has already been modified by another transaction (that committed since the initial read).
  • Dirty read : A transaction when reads data that is written by a concurrent uncommitted transaction is the dirty read.


A sequence of characters bound by single quotes is contained by string constants. This feature is used when one needs to insert a character or to pass a character to database objects. PostgreSQL allows the usage of single quotes but embedded by a C style backslash. A string constant is a sequence of characters bound together by single quotes instead of double quotes, which is generally the case with string type variables. This feature is mostly used when a character is being inserted or when a character needs to be passed to database objects. This feature is exceptionally important while parsing data. PostgreSQL lets a user use single quotes only when it is embedded by the specific C-style backslash.
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.
 Following are some of the advantages of PostgreSQL :
  • Stable
  • Reliable
  • Extensible
  • Easy to learn
  • Open source
  • Designed for High Volume Environments
  • Cross Platform
  • Better Support
  • Flexible
Tokens are the building blocks of any source code. They are known to comprise many of the special character symbols. These can be regarded as constants, 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.

It is not that hard as it seems. To get your statistics updated in PostgreSQL a special function called explicit ‘vacuum’ call is made. The method to do is to create Vacuum where the option of Analyze is used to update statistics in Postgresql


is the syntax.