PostgreSQL Interview Questions

PostgreSQL is a relational, open-source, and lightweight database. Due to its proven architecture, data integrity, reliability, and integration with programming languages like R and Python, PostgreSQL is highly accepted by the industry, with enterprises of all sizes using it. Big tech organizations like Cisco and Apple are using PostgreSQL in the back-end applications.

Thus, due to its huge popularity, there will be massive job opportunities in PostgreSQL and you can build a promising career. To help you in the interview process, we have curated the most common PostgreSQL interview questions with answers for all experience levels.

Table of Contents

• PostgreSQL Interview Questions
  
  • For Freshers
  • For Intermediate
  • For Advanced
• Frequently Asked PostgreSQL Interview Questions

Top 10 PostgreSQL Interview Questions

1. Define a Join in PostgreSQL.
2. What are the primary constraints of PostgreSQL?
3. Describe Triggers
4. Explain PostgreSQL Architecture?
5. How do we install PostgreSQL?
6. How can we provide security in PostgreSQL?
7. How do we use the JSON data in PostgreSQL?
8. How do we perform the data migration?
9. What are the different kinds of Indexes?
10.  What are the differences between PostgreSQL and SQL?

PostgreSQL Interview Questions

Let’s go through important PostgreSQL Interview Questions and Answers at various expertise levels.

PostgreSQL Interview Questions for Freshers

1. What is PostgreSQL?

PostgreSQL is the freeware object-relational database management called ORDBMS. It is also called Postgres. It is one of the most popular and widely utilized Object-Relational Database Management Systems. It is a strong database management system that offers substantial and additional power by integrating fundamental concepts so that users can extend the database without any problem.

If you want to enrich your career and become a professional in PostgreSQL, then enrol in "PostgreSQL Online Training". This course will help you to achieve excellence in this domain.

2. What are the primary applications of PostgreSQL?

PostgreSQL enables you to

• Create, Update, and Delete the tables in the Database
• Manipulate, Modify, and Access the Data in a table
• Summarize and Retrieve the required information from a single table or multiple tables
• Remove or Add particular rows or columns from the table

3. How can we add new values to a particular table?

PostgreSQL utilises the “INSERT INTO” statement for adding data to your SQL table.

4. What are the methods PostgreSQL provides to create a new database?

PostgreSQL provides the following methods to create a new database

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

5. How do you delete the database in PostgreSQL?

We can delete the database by using any one of the below options:

• Using DROP DATABASE, an SQL command
• Using dropdb

Related article: Comparison Between MongoDB and PostgreSQL

6. What is a Schema?

A database schema includes the visual and logical configuration of the complete relational database. In the PostgreSQL, a schema contains tables with views, datatypes, indexes, constraints, functions, and sequences.

7. What does a schema contain? 

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

8. Define a Join in PostgreSQL.

Joins are used for combining and retrieving the records from two or more tables. PostgreSQL utilizes SQL joins for performing these types of operations.

9. Define a Constraint in PostgreSQL.

A group of conditions defining the kind of data that acts as input to every column of the table. Constraints will be used for assuring the data integrity in the table and avoid unnecessary actions.

10. What are the different operators in PostgreSQL?

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

11. What is the difference between a primary key and a foreign key in PostgreSQL?

A Primary Key enables only a unique value and non-null values, whereas a foreign key offers shared keys between two or more tables.

12. What are the primary constraints of PostgreSQL?

PostgreSQL offers the following constraints:

1. Not-Null Constraints
2. Unique Constraints
3. Check Constraints
4. Foreign Keys
5. Primary Keys
6. Exclusive Constraints

13. What are the different kinds of Joins in PostgreSQL?

1. Inner Join: It returns the records that have matching values in both the tables
2. Right Join: It returns all the records from the Right Table and the matched records from the left table.
3. Left Join: It returns all the records from the Left Table and matched records from the right table.
4. Full Join: It returns all the records when there is a match in either the left or right tables.

14. What is a View?

The view depicts the query result to one or multiple inherent tables. Views are used to simplify difficult queries as these queries are defined once in the view and can be directly queried.

15. Explain Normalization.

In Database, Normalization is a mechanism through which we can create or modify the databases and tables for handling the inefficiencies related to data storage, querying processes, or data modification. In other terms, normalization includes multiple steps for reducing data complexity and redundancy.

16. Describe Triggers

Triggers, also called as the callback function, is the specification that a database must automatically implement a specific function whenever a particular kind of operation is carried out. We can define the triggers for executing either before or after the INSERT, UPDATE, or DELETE operation, either once per SQL statement or once per the modified row. If the trigger event happens, the trigger’s function is invoked at the proper time for handling the event. Triggers allow you to ensure the data integrity while modifying the database.

17. How can we select the first seven rows in the table called “employees” in the PostgreSQL?

By executing the following query, we can select the first seven rows in a table:

SELECT * from employees LIMIT 7;

18. Explain PostgreSQL Architecture?

PostgreSQL utilizes the client-server model to receive the request from the end user, process it, and return it to the client. It is a process per-user client-server model in which a new process will be started for every client connection request, and the PostgreSQL server process processes the client request. The PostgreSQL server process will perform all the operations in support of the client process. 

Components of PostgreSQL Architecture

1. Postmaster Supervisor Process

Postmaster serves as the supervisor in PostgreSQL architecture, and it is the first process that will start after PostgreSQL starts. It serves as the Listener and is accountable for authorizing and authenticating the incoming request from client and allocating a new method called postgres for every connection. It also monitors the process and starts if it is dead.

2. Shared Memory Segments

Shared Memory Segments are buffer caches in the memory that are reserved for transactions and maintenance activities. There are various shared memory segments assigned for performing a different operation. 

3. Background process of PostgreSQL

The background processes are the crucial components of the PostgreSQL database. These processes are used for maintaining the consistency between the disk and memory, and because of this, PostgreSQL will work properly. Every PostgreSQL background process will play its role. The following is the list of background processes:

• Checkpointer
• Background Writer
• WAL Writer
• Statistics Collector
• WAL Writer
• Physical Files

The Physical Files are used for storing the actual data in the form of the data files, the Archive log information, the server log details in log files, the changed blocks in the WAL files, etc. The data in the files are stored permanently and are utilized for their corresponding operation.

The following are the physical files in PostgreSQL:

1. WAL Files
2. Data Files
3. Log Files
4. Archive Logs

19. What is a Primary Key?

In PostgreSQL, the primary key is the column or group of columns uniquely identifying every row in the table. It assures the integrity and uniqueness of the data in the table. The primary key constraint applies the rules below:

• The values of the primary key columns should be unique.
• The primary key columns must not include null values.

For defining the primary key in the PostgreSQL, we can utilize the “PRIMARY KEY” constraint while creating or altering the table for adding the constraint. We can define only one primary key per one table.

20. How do we install PostgreSQL?

For installing PostgreSQL, we have to follow the below steps:

1. Go to official PostgreSQL website and download the installer ideal for your operating system.
2. Execute the installer and follow on-screen instructions. We may have to specify the installation directory and give a password for database superuser.
3. Choose the components you have to install, like PostgreSQL server, graphical interface, and command-line tools.
4. Finish the installation process and ensure that PostgreSQL service has begun.
5. Alternatively, configure the additional settings like memory allocation or network access as per your requirements.

Related article: How to Install PostgreSQL?

21. What are the benefits of PostgreSQL?

There are several benefits of using PostgreSQL

1. It offers excellent scalability and performance, efficiently managing massive amounts of data and parallel connections.
2. It provides various advanced features, like support for complex data types, geospatial data, and full-text search.
3. PostgreSQL is highly scalable, enabling developers to create the custom data types, procedural languages, and functions.
4. It supports data integrity, reliability and ACID properties.

22. What are the important features of PostgreSQL?

1. It endorses all the main operating systems.
2. PostgreSQL is the object-relational database
3. It also supports procedural languages and multi-version concurrency control(MVCC).
4. PostgreSQL also includes Nested transactions.

23. Explain Transaction?

• In PostgreSQL, a transaction is a sequence of database operations considered as a single logical unit. It assures the atomicity, isolation, durability, and consistency properties of a group of associated database engines. Transaction enables multiple database operations to be implemented together. If any part of the transaction fails, all the modifications within the transaction can be rolled back, maintaining the data integrity.
• In PostgreSQL, transactions can be handled internally through the auto-commit mode, where every statement is considered as a separate transaction, or eternally through the BEGIN, ROLLBACK, and COMMIT statements for defining the transaction boundaries.

24. What is a Foreign Key?

In PostgreSQL, a Foreign Key is a column or group of columns that sets up the link between two tables. It depicts the relationship between the referenced table(parent table) and the referencing table(child table). The foreign key assures the referential integrity, applying the rules below:

• The values in foreign key columns should be available in the primary key or unique key constraint of the referenced table.
• Deletions or Updates in referenced table are controlled for maintaing the consistency in referencing table.

For defining the foreign key in PostgreSQL, we can utilize the foreign key constraint while altering the table or creating the table for adding the constraint. The foreign key columns in referencing table should have same data type as primary key columns in referenced table.

25. Can we run PostgreSQL on the Cloud?

Yes, we can run PostgreSQL on the most famous cloud providers like AWS, Google Cloud, and Azure.

26. Explain Multi-Version Concurrency Control

Multi-Version Concurrency Control is the advanced technique of PostgreSQL. It improves the database performance in the multi-user scenarios. This indicates that when we query the database, every transaction views a snapshot of the database since it was some time ago, irrespective of the present state of inherent data. This secures the transaction from seeing the inconsistent data that concurrent transaction updates on the similar data rows can induce.

27. How can we create a backup of the database in PostgreSQL?

Creating a backup of your database in PostgreSQL is simple. There are several methods for performing a backup in PostgreSQL like On-line backup, SQL dump, and File system-level backup.

28. What are the advantages of Partitioning?

Partitioning enables you to divide the table into smaller, more manageable partitions, which convert into improved query performance. It’s specifically ideal while handling massive tables.

29. What commands do we need to execute to control the transactions in the PostgreSQL?

There are three primary commands for controlling the transactions in the PostgreSQL

1. BEGIN TRANSACTION or BEGIN: For starting a transaction
2. ROLLBACK: It is used for undoing the transactions that are not saved to a database.
3. COMMIT or END Transaction: For saving the changes. The “COMMIT” command saves all the transactions to the database as the last COMMIT or the “ROLLBACK” command.

30. What purpose does pgAdmin in the PostgreSQL server have?

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

31. What is PL/Python? 

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

32. How can we enhance the query performance in the PostgreSQL?

The following are the different strategies to enhance the query performance:

1. Through indexing, particularly in queries that include WHERE clauses.
2. Performing Partitioning for the large tables.
3. Developing SQL statements for reducing the processing overhead, for instance, by preventing the unrequired columns in the”SELECT” statement.
4. Maximizing the memory utilization by tuning the server parameters for matching the hardware specifications.

33. How can we handle the errors in the PostgreSQL?

In PostgreSQL, to handle errors, we have the following ways:

• Callback functions can be built for handling the error and warning conditions. In this case, we can define a particular behaviour in case of warnings and errors in the queries through the “WHENEVER” method.
• Detailed information about the warning or error can be achieved from the SQL variable. This variable offers in-depth information while warnings and errors arise during the execution.

34. What are database callback functions called? What is its purpose?

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

PostgreSQL Interview Questions for Intermediate Professionals

35. What does a Cluster index do? 

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

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

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

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

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

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

Though the DROP TABLE command has the ability to delete complete data from an existing table, the disadvantage with it is - it removes the complete table structure from the database. Due to this, we need to re-create a table to store data.

39. What is the most rapid way to remove all the rows in a huge table?

There are two primary ways for removing the rows in the table: the TRUNCATE command and the DELETE command. The former is developed to remove rows more wisely and needs a complete scan of the tables. The latter rapidly all the rows and empty disks without table scan. Thus, the TRUNCATE command is the most ideal one.

40. How can we provide security in PostgreSQL?

In PostgreSQL, Security is addressed on various levels:

• File Protection in Database: All the files stored in the database are secured from reading by the account other than PostgreSQL superuser account.
• Client Connections can be limited to a username or IP address.
• Connections from the client to the database server are, by default, enabled only through the local unix socket.
• Client Connections can be authenticated through the external packages.
• Each user in PostgreSQL is assigned a username and a password.
• Users can be assigned to the groups, and table access can be limited per group privileges.

41. How can we delete a table and other objects related to it, like views, functions, triggers, and stored procedures?

For deleting a table in the PostgreSQL, use “DROP TABLE” command, followed by the name of the table. For deleting any other object related to it, we have to add “CASCADE” command.

42. What is the importance of logs for troubleshooting?

PostgreSQL logs are a valuable resource to troubleshoot the problems, audit the database activity, and track performance. PostgreSQL contains a broad variety of logs, like error logs. These logs can allow you to identify the queries and statements that cause errors during the execution.

43. When do we use “EXPLAIN ANALYZE” command in PostgreSQL?

The “EXPLAIN” command displays the execution plan of the SQL statement. This contains the way the tables referenced in our statement will be processed, the inherent algorithms used for difficult operations, like joins and the estimated execution time.

Besides the estimated time, if you have to know the actual time needed, you can add the “ANALYZE” command, and the statement will be executed, not planned. The “EXECUTE ANALYZE” command is used for identifying the problems in the difficult queries so that we can rewrite them for enhancing the query performance.

44. What is the use of “pg_dump” method?

The “pg_dump” method enables you to create the text file with a group of SQL commands that, when we run in the PostgreSQL server, will recreate database in the same state since it was at the time of dump.

45. What will be the maximum table size for a table in the PostgreSQL?

In PostgreSQL, the maximum size for a table is 32 TB.

46. How can we create an index in PostgreSQL?

In PostgreSQL, we will use the “CREATE INDEX” statement for creating the index. Here is an example:

CREATE INDEX Emp_Index ON Employee(Emp_ID, Emp_Name, Emp_Salary);

The above statement will create index on “Employee” table.

47. Explain Composite Type

In PostgreSQL, Composite Type enables you to define the custom data structures that can store multiple values of the different data types. It allows you to create the user-defined types made up of the available data types. Composite types are helpful when grouping the associated data elements into one entity. To define the Composite type, we can utilize the “CREATE TYPE” statement. For example:

CREATE TYPE country_type as(state VARCHAR, city VARCHAR, District VARCHAR);

In the above example, the country_type composite type includes three fields: state, city, and district.

48. How can you delete complete data from an existing table?

We can delete complete data from an existing table using the PostgreSQL TRUNCATE TABLE command.

49. What are the different properties of a transaction in PostgreSQL? Which acronym is used to refer to them?

The properties of a transaction in PostgreSQL include Atomicity, Consistency, Isolation, and Durability. These are referred to by the acronym, namely ACID. 

50. What purpose does the CTIDs field serve?

The CTIDs field identifies the specific physical rows in a table according to their block and offsets positions in that table.

51. Which are the commands used to control transactions in PostgreSQL?

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

52. How can we handle the Concurrent updates?

PostgreSQL manages the concurrent updates using its MVCC(Multi-Version Concurrency Control) mechanism. It enables multiple transactions to use the same data simultaneously without causing conflicts or blocking each other.

When two transactions try to modify same data concurrently, PostgreSQL assures isolation by creating separate data copies for every transaction. In this way, every transaction sees the consistent snapshot of data as it showed up at the starting of transaction. PostgreSQL offers different isolation levels and locking mechanisms for handling concurrent updates if any conflicts happen. 

Developers will select proper transaction isolation levels like REPEATABLE READ, READ COMMITTED, and SERIALIZABLE per their application’s needs and exchanges between data consistency and concurrency.

53. Describe Materialized Views

In PostgreSQL, a materialized view is the database object that stores the results of the query as a physical table. In contrast to regular views, which are virtual and execute inherent queries every time they are used, materialized views are updated and precomputed manually or periodically.

For creating the materialized view, we can utilize the “CREATE MATERIALIZED VIEW” statement, declaring the query that defines the contents of the view. The materialized view is formulated with a query when it is refreshed or created.

They are helpful when you have difficult and resource-intensive queries that are executed regularly. However, their inherent data only changes slowly. By storing and precomputing results, we can achieve major performance enhancements while querying materialized views.

54. How can we perform bulk interests?

For performing the bulk inserts effectively, we can utilize the “INSERT INTO SELECT…” statement or “COPY” command.

1. INSERT INTO … SELECT statement

INSERT INTO table_name(column1, column2, …) SELECT value1, value2,... UNION ALL SELECT value1, value2, ….

Through the INSERT INTO … SELECT statement, we can insert multiple rows in a single SQL statement. Define the columns and their respective values through the “SELECT” clause, repeating “SELECT” statement for every row we have to insert. This method is used when we have to insert the data generated dynamically or from another table.

2. COPY Command

COPY table_name(column1, column2,...) FROM ‘data_file’ WITH(FORMAT csv);

“COPY” command will read the data from the file given by “data_file” and insert it into specified table. The file must include data in the format that matches the given format. This method is rapid and useful for huge datasets.

55. Describe Stored Procedures

A Stored Procedure is pre-compiled, and the stored database object that binds a set of SQL statements. It enables you to carry out difficult operations and implement them as a unit. The advantages of utilizing stored procedures are code reusability, improved security, and enhanced performance.

For creating the stored procedure, we can execute CREATE PROCEDURE or CREATE FUNCTION statements. A stored procedure will have the input and output parameters, control flow logic and local variables through the loops and conditionals. It will also return the result sets through the “OUT” or “RETURN TABLE” parameters.

56. How do we create a view?

For creating a view in the PostgreSQL, we have to use the "CREATE VIEW" command. Example:

CREATE VIEW view1 as select * from emp where dept_id = ‘HR’

The above view is created for employees of the 'HR' department in the "emp" table.

57. What is the difference between CTE and Subquery?

The primary difference between CTE and Subquery is their usage and structure.

• CTE: A CTE is the temporary result set defined in the query. It is created using "WITH" clause and can be referenced multiple times in the same query. It enhances query readability and enables recursive queries. They are more useful when the complex query needs multiple subqueries for sharing a common table.
• Subquery: A Subquery is the nested query in another query. It is created in the parenthesis and can be utilized in the "WHERE ', "HAVING", or "FROM" clauses. Subqueries are assessed first, and their results can be utilized in the outer query. Subqueries cannot be reused and can impact query performance when used extremely.

58. Differentiate "UNION" and "UNION ALL"

Both UNION ALL and UNION are used for combining the results of the multiple "SELECT" statements. But, they differ in terms of their result sets and behaviour.

• UNION ALL: The "UNION ALL" operator combines results of multiple "SELECT" statements but will not remove the duplicate rows. It contains all the rows from every "SELECT" statement, containing duplicates. This operator is more rapid than the "UNION 'statement because it does not need duplicate elimination.
• UNION: The "UNION" operator will combine the results of multiple "SELECT" statements and reduce the duplicate rows from the final result set. It carries out a distinct operation, assuring that the unique rows are returned. This operation will have overhead because of the duplicate elimination.

59. How do we implement the table partitioning?

Table Partitioning will allow you to split the large table into small, manageable pieces known as partitions. Every partition stores the subset of the data as per the specified partitioning key. To implement the table partitioning, follow the below steps:

• Create the parent table with all the required columns, like the partitioning key.
• Create the child table that will be inherited from the parent table. Every child table represents a particular partition.
• Define the constraints on every child table for limiting the partitioning key values.
• Create the indexes on the child tables for optimizing the query performance.

The partitioning feature of PostgreSQL offers automatic routing of data to the proper portions as per the partitioning key, leading to simplified data management and enhanced query performance.

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

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

61. What does Write-Ahead Logging do?

Write-ahead logging enhances database reliability by logging changes before any changes or updates are made to the database.

62. What are some of the important data administration tools supported by PostgreSQL?

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

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

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

64. What is a non-clustered index?

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

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

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

66. Are there any disadvantages with  PostgreSQL?

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.

Related article: MySQL Vs PostgreSQL Performance

67. What does a token represent in a SQL Statement?

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

68. How do we use the JSON data in PostgreSQL?

PostgreSQL has excellent support to work with the JSON data. We can store, manipulate, and query the JSON documents through different parameters and functions. For storing the JSON data, we can utilize the JSON and jsonb data types. The jsonb offers the binary storage and provides querying and indexing capabilities. 

For querying the JSON data, PostgreSQL offers various functions like jsonb_array_elements , jsonb_extract_path, and jsonb_agg. These functions enable you to extract particular values, navigate through the JSON arrays and objects, and aggregate the JSON data. We can also use operators like -> and → for accessing the JSON values and fields directly in the SQL queries. Moreover, PostgreSQL endorses the indexing on the JSONB columns, enabling effective querying of the JSON data.

69. What is the use of "VACCUM" in the PostgreSQL?

In the PostgreSQL, VACCUM is a critical process to handle and reclaim the disk space occupied by outdated or deleted data. It performs two primary tasks:

• Updating the Statistics: VACCUM analyzes distribution of the data and updates statistics utilized by query planner. Exact statistics enable PostgreSQL to select optimal query plans, leading to enhanced performance.
• Releasing the disk space: When the data is deleted or updated in PostgreSQL, it is not instantly removed from the disk. Rather, it becomes marked as reusable by the future inserts. The VACCUM process will identify the reusable pages and make the space available for future purposes.

70. How do we implement Replication?

PostgreSQL endorses several methods to implement replication to assure data redundancy and high availability. The two primary replication methods of PostgreSQL are as follows:

1. Physical Replication: This method includes creating the exact copy of main database by constantly streaming write-ahead logs to multiple standby servers. The standby servers will be used for the read-only queries since failover targets if the primary server becomes unavailable.

Streaming Replication is easy to set up and offers real-time applications with low latency.

2. Logical Replication: Logical Replication will replicate the modifications made to particular databases or tables rather than replicating the complete database cluster. It utilizes the publications, subscriptions, and slots for defining what data must be replicated and where. Logical Replication offers more granularity and flexibility but needs monitoring and configuration.

PostgreSQL Interview Questions for Advanced Professionals

71. Describe full-text search

In PostgreSQL, full-text search allows you to perform advanced the text indexing and searching. It is specifically useful to search massive sets of natural language or unstructured text. PostgreSQL offers the tsquery and tsvector data types for handling the full-text searches. The tsvector type depicts the document's textual content, whereas tsquery type depicts search query.

For performing the full-text search, we have to create the full-text search index on the required column through the "CREATE INDEX" statement with "USING" method. After that, we can use the "@@" operator for matching the search query against indexed column.

72. How do we perform the data migration?

In the PostgreSQL, we will perform the data migration using the following steps:

1. Create target database: First, create an empty target database where we have to migrate data.
2. Export source data: Through the "pg_dump" utility, we can export the data from source database into the file. We can specify the required format, like custom binary or plain SQL.
3. Transfer data: Copy exported file to server hosting target database or transfer it to a destination system.
4. Import data: Through the PSQL command-line tool or pg_restore utility, we can import the data into the intent database. If you are using the "pg_restore", specify proper options and file including exported data.
5. Verify Migration: Carry out the data integrity checks and compare migrated data with source data for ensuring a successful migration.

73. Differentiate Regular Views and Materialized Views

The primary difference between regular and materialized views is how they store and handle the data.

• Materialized Views: Materialized Views store the results of inherent data in the physical table-like structure. The data is stored and computed while creating and refreshing periodically. Materialized views are more useful when inherent data is exorbitant to compute or when view data have to be indexed for the fast retrieval.
• Regular Views: In PostgreSQL, regular views are the virtual tables specified by the query. They will not store any data but will dynamically fetch it from inherent tables whenever the view is queried.

Selection between regular views and materialized views depends on particular use cases and the frequency of the data updates.

74. How do we perform the logical Replication?

For performing logical Replication, we have to follow the below steps:

• Enable logical operation feature by setting the "wal_level" configuration parameter to the logical in postgresql.conf file.
• Create the publication on source database through "CREATE PUBLICATION" statement. This will define the tables or schemas that can be replicated.
• Create the subscription on target database through "CREATE SUBSCRIPTION" statement. Specify connection information for source database and publication to replicate.
• Begin replication process by implementing "ALTER SUBSCRIPTION" statement with "ENABLE" option.

After that, PostgreSQL will replicate the table or schemas from source database to target database, enabling you to maintain them synchronized.

75. How do we implement the parallel query execution?

For implementing the parallel query execution, we can follow the below steps:

• Assure that the max_parallel_workers configuration parameter is set to a value greater than the zero in Postgresql.conf file. This decides the maximum number of parallel workers existing for the query execution.
• Adjust max_parallel_workers_per_gather configuration for controlling the number of parallel works used per query gather mode. This allows you to restrict parallelism for individual queries.
• Set the min_parallel_index_scan_size and min_parallel_table_scan_size configuration parameters for controlling the minimum index or table size needed for the parallel scans to be considered.
• If required, we can manually disable or enable parallel execution for particular queries through the SET max_parallel_workers_per_gather statement or by modifying the index or table settings with "ALTER INDEX" or "ALTER TABLE."

By configuring these settings and using the parallel-safe operators. PostgreSQL will parallelise the query execution throughout multiple orders, resulting in quicker query performance.

76. What are the different kinds of Indexes?

PostgreSQL supports the following kinds of Indexes:

1. Hash Index: Effective for equality-based lookups but not ideal for range queries.
2. B-tree Index: This is the default index type, ideal for equality conditions and range queries.
3. Generalized Inverted Index(GIN): Suitable for full-text search and arrays.
4. Generalized Search Tree(GIST) Index: It is used for several data types and endorses different operators, like text or spatial search.
5. SP-Gist(Space-Partitioned Generalized Search Tree) Index: It is suitable for the custom data types and endorses several search strategies.
6. Block Range Index(BRIN): It is developed for large tables that store sorted data, enabling effective scans by partitioning data into blocks.
7. Bloom Filter Index: It offers estimated data matching, which is helpful for massive datasets.

Every index type will have its benefits and is ideal for various scenarios. The index type selection is based on your data's particular characteristics and requirements.

77. What is the use of pg_stat_activity view?

In PostgreSQL, the pg_stat_activity view offers information about the server's currently running activities. It includes a row for every session linked to database and contains details like username, process ID, application name query being executed, and other statistics.

It is generally used for monitoring the database server, checking idle or blocked connections, identifying long-running queries, and gathering performance-related information. By querying this view, administrators will get insights of current activity and the state of database, enabling them to troubleshoot issues, optimize performance, and handle connections efficiently.

78. Describe Recursive Query.

In PostgreSQL, a Recursive query is a kind of query that references its outputs. It enables you to carry out the repetitive operations or traverse graphical or hierarchical-like structures. They are built through the "WITH RECURSIVE" clause, which is also called common table expression(CTE). CTE includes two parts: the anchor member, which serves as the base case and the recursive member, which develops on the result of the previous iteration. 

The recursive member will refer to CTE itself, enabling you to query iteratively until a particular condition is satisfied. This recursion will enable you to perform hierarchical queries, traverse the tree structures, and handle the recursive data relationships.

79. What are the differences between PostgreSQL and SQL?

PostgreSQL is considered as the advanced version of SQL. Following are some differences between these PostgreSQL and SQL:

1. In contrast to SQL, we cannot update views in PostgreSQL.
2. Like SQL, PostgreSQL does not provide computed columns.
3. Contrary to SQL, in PostgreSQL, you don’t have to create the DLL for seeing what the code is doing.
4. PostgreSQL endorse dynamic actions, while SQL does not endorse them.

80. What is the primary difference between lock and multi-version models?

A multi-version model enables multiple versions of the same data to existing parallel, whereas a lock model only enables one version of the data to be available at a time and locks the data while it is edited.

81. What is a Sequence?

In PostgreSQL, a sequence is the database object that creates a sequence of unique integers that can be utilized as default values for the column or as part of the primary key.

82. What is a tablespace?

A tablespace is a location or the disk where the data files of particular tables or indexes can be stored, enabling more control of disk utilization and file placement.

83. How do we create and handle the user-defined functions?

For creating and handling the user-defined functions, we can utilize “CREATE FUNCTION” statement. Example:

CREATE FUNCTION function_name(Argument1, Argument2) RETURNS return_type  AS $$BEGIN 

Function Logic

END

We can replace the function_name with the function name. Declare the return types and argument types as per your requirements. Function logic will be written within the BEGIN and END blocks. For calling the function, we will use the following statement:

SELECT function_name(argument1, argument2);

84. What is the use of pg_stat_replication view?

The pg_stat_replication offers the information on the activity and status of the standby servers in the streaming replication setup. By using this view, we can get the following details:

• Standby server name and connection information
• Replication lag between the standby and primary servers.
• Received and Applied for WAL positions
• Replication state

This view is used to monitor the synchronization and health status of the standby servers and assuring the overall stability of replication setup.

85. How do we implement Sharding?

Sharding refers to horizontally partitioning data throughout the multiple shards or servers for distributing the load and scaling the database system. To implement the Sharding, we have to follow the following steps:

1. Set up shard servers: Create the individual PostgreSQL clusters or instances for every shard. Every shard must have its servers, like its storage, processing, and memory capacity.
2. Determining the Shard strategy: Select a strategy to partition the data throughout multiple shards. General strategies like hash-based sharding, range-based sharding, or a combination of both.
3. Implementing the application logic: Modify the application code and use middleware to route the data and queries to the proper shard as per the data distribution rules.
4. Defining the data distribution rules: Determine how to distribute the data throughout the shards as per the selected sharding strategy.
5. Managing data synchronization and consistency: Implementing mechanisms for ensuring data consistency throughout the shards, like logical replication, data synchronization, and distributed transaction tools.

86. How do we implement the row-level security?

In PostgreSQL, Row-level security enables you to limit the access to the rows in the table as per specific policies or conditions. To implement the row-level security, we have to follow the following steps:

• Enable the row-level security feature by setting up the row_security configuration parameters for postgresql.conf file or utilizing the ALTER TABLE for the individual files.
• Define the security policy on the table through the “ALTER TABLE” statement with “ENABLE ROW LEVEL SECURITY” clause. This relates to the table with the security policy name.
• Create the security policy through the “CREATE POLICY” statement, declaring the conditions that decide which rows can be modified or accessed. We can utilize the column values, custom functions, or user roles for defining the policy rules.
• Give proper privileges to the database roles through the “GRANT” statement, enabling them to access the table with the specified security policies.

After implementing the row-level security, PostgreSQL will automatically apply security policies whenever queries are implemented on the related table.

87. How do we implement the data encryption?

We can use the following techniques to implement data encryption:

1. Column-level Encryption: This technique encrypts sensitive data elements or columns in the database. We can utilize the “pgcrypto” extension for encrypting particular columns through the cryptographic algorithms and functions.
2. TDE(Transparent Data Encryption): It encrypts the data at storage level, making it transparent to users and applications. By allowing the TDE on the file system or utilizing hardware encryption, all the data stored in PostgreSQL will be encrypted on the disk.
3. TLS/SSL Encryption: PostgreSQL endorses encrypting client-server communication through the SSL/TLS Encryption. By enabling the SSL/TLS and configuring the required certificates, we can secure the data transit.
4. Application-Level Encryption: Encrypting data at the application level includes encrypting data before it is stored in the database and decrypting it when retrieved. This approach gives you complete control on key management, access control, and encryption algorithms.

88. What three phenomena should be prevented between the concurrent transactions?

The three phenomena that should be prevented between the concurrent transactions are: 1) Dirty Reads, 2) Lost updates, and 3) Inconsistent Reads.

89. What are the main differences between PostgreSQL and Oracle?

PostgreSQL	Oracle
PostgreSQL is an open-source and free object-relational database management system that uses SQL extensibility and standards.	Oracle is an object-relational database management system. It is the first database management developed for grid computing.
It is developed and implemented in C Language.	It is developed and implemented in C++, C, and assembly language.
In comparison to Oracle, PostgreSQL is a new database. It was designed by PostgreSQL Global Development Group on 8th July 1996.	In Comparison to PostgreSQL, Oracle is an old database. It was designed by Bob and Larry Ellison.
PostgreSQL offers good security support but less in comparison to Oracle.	Oracle offers advanced security options.
PostgreSQL is free to use and open-source.	To use Oracle, you need a license.

Related article: PostgreSQL vs Oracle

90. What are the differences between MongoDB and PostgreSQL?

MongoDB	PostgreSQL
It is a NoSQL Database.	PostgreSQL is the classic relational database system that endorses all the SQL standards.
It is developed in C++ programming.	It is developed in C language.
It is a non-relational database management system.	It is a relational database management system.
MongoDB is a Document Oriented Database.	PostgreSQL is an Object-Oriented Database
It is available only in the English Language.	It is available in Multiple Languages.

Frequently Asked PostgreSQL Interview Questions

1. What is the latest version of PostgreSQL?

The latest version of PostgreSQL is PostgreSQL 16.3, released on 9th May 2024.

2. What are the new features of PostgreSQL?

The new features of PostgreSQL 16.3 are as follows:

1. pg_stat_io - I/O metrics view
2. ANY_VALUE Aggrgeate in SQL
3. Non-decimal integer literals
4. Underscores(_) for thousand separators
5. Load Balancing for psql/libpq
6. Parallel Right and Full Joins
7. SIMD support for x86 and ARM
8. JSON/SQL Constructors

3. What are the job responsibilities of a PostgreSQL Developer with 2-3 years of experience?

• Create and Maintain Databases, Tables, and Views
• Build high-quality Stored Procedures
• Work with front-end developers to define simple and strong APIs
• Optimize database queries and assure table deadlocks or locking happen
• Excellent Understanding of ETL and ELT concepts.

4. What are the job responsibilities of a PostgreSQL Developer with 3-5 years of experience?

• Install, Maintain, and Monitor PostgreSQL Server
• Assisting in Business Process Integration with several data sources
• Implementing Backup and Recovery Processes
• Setting up PostgreSQL Clusters and Supporting Database clusters in on-prem and hybrid environments.
• Implementing Postgres STIG and Testing

5. What are the Job responsibilities of a PostgreSQL Developer with more than five years of experience?

• Migrating to PostgreSQL from other RDBMS
• Optimizing Postgres Instances
• Implementing the best practices for DR, High Availability, Upgrades, and Backup
• Troubleshooting Performance Issues
• Implementing High-Performance strategies like Message Queuing and Full Text Indexing.

6. What are the secondary skills required for a PostgreSQL Developer?

Along with an expert-level knowledge of PostgreSQL, a PostgreSQL Developer also requires a good understanding of Unix scripting, JSON, SQL, and any programming language like Python.

Conclusion

PostgreSQL is a famous database used by different tech giants to store data and maintain back-end applications. These PostgreSQL Interview Questions will evaluate their knowledge and prepare you for job interviews. I hope these questions will help you for your career advancement. If you have any queries, let us know by commenting below.