Top 40+ PostgreSQL Interview Questions and Answers for Practice
Tejasvee Sharma
Jan 26, 2022
If you are looking for PostgreSQL Interview Questions then you are at the right place. Here you will find the list of the top 40 PostgreSQL Interview Questions and Answers which are generally asked in job interviews. Freshers, experienced, and experts of all kinds of candidates can go through this article as it has all the types of questions for all level candidates. If you are specifically appearing for an SQL job interview then you should prepare from these PostgreSQL Interview Questions and Answers for a better understanding of SQL.
About PostgreSQL: Postgres is simply known as Postgresql in the SQL. PostgreSQL is a strong open source object-relational database management system that creates and uses the advanced and extended SQL language combined with many elements that safely store and work with complicated data. It is used in making a large web application.
It is one of the widely used Object-Relational DBMS that helps in developing large web applications. It is a powerful, open-source object-relational database system that gives additional and significant power by incorporating four fundamental concepts in such a way that the user can expand the system without any trouble. It extends and operates the SQL language that is mixed with different features to safely scale and reserve the complex data workloads.
2. Name some features of Postgresql?
Supports major Operating systems
Object-relational database
Multi-version concurrency control (MVCC) and Procedural languages
Table inheritance & Asynchronous replication
Flexible API and Database validation
Support Extensibility for SQL and Complex SQL queries
Nested transactions
WAL and Client-server
3. Name various datatypes of Postgresql?
UUID
Numeric types
Boolean
Character types
Temporal types
Geometric primitives
Arbitrary precision numeric
XML
Arrays etc.
Users can also make their indexes and get them indexed.
4. Tell me the objective of pgAdmin in PostgreSQL server?
It is basically a data administration tool. It performs the objective of developing, retrieving, maintaining, and testing databases.
5. Explain PL/Python?
PL/Python is a technical language to which PostgreSQL gives support.
6. Which are the techniques PostgreSQL uses to construct a new database?
PostgreSQL uses the following techniques to construct a new database:s
Using CREATE DATABASE, an SQL command
Using created a command-line executable
7. Tell me the way to delete the database in PostgreSQL?
By using any one of the below-given options, we can delete the database in PostgreSQL:
Using DROP DATABASE, an SQL command
Using dropdb a command-line executable
8. What does a schema have?
A schema has tables along with views, data types, operators, indexes, functions, and sequences.
9. Name the different operators in PostgreSQL?
The PostgreSQL operators contain - Arithmetic operators, Logical operators, Comparison operators, and Bitwise operators.
10. What is the name of database callback functions and what purpose does it serve?
The database callback function is named PostgreSQL Triggers. When a selected database event happens, the PostgreSQL Triggers are executed or invoked automatically.
11. Tell me the use of indexes?
Search engines use the indexes to speed up data retrieval
12. Tell me the use of Cluster index?
Cluster index categorizes table data rows on the basis of their key values.
13. What are the advantages of selecting data types in columns while making a table?
Some of these advantages are consistency, validation, compactness, and performance.
14. What do you require to update statistics in PostgreSQL?
We require using a special function known as a vacuum to update statistics in PostgreSQL.
15. What is the drawback of the DROP TABLE command in deleting entire data from a current table?
By using the DROP TABLE command you can delete entire data from a current table, but the drawback with it is - it eliminates the entire table format from the database. This leads to re-creating a table to store data.
16. Tell me the way to delete the entire data from the current table?
We can delete the entire data from the current table operating the PostgreSQL TRUNCATE TABLE command.
17. Tell me the properties of a transaction in PostgreSQL?
Atomicity, Consistency, Isolation, and Durability (ACID) are the properties of a transaction in PostgreSQL.
18. What objective does the CTIDs field serve?
The CTIDs field determines the precise physical rows in a table as per their block and offsets positions in that table.
19. Name the commands used to handle transactions in PostgreSQL?
BEGIN TRANSACTION, ROLLBACK, and COMMIT are the commands used to handle transactions in PostgreSQL.
20. Differentiate between SQL and PostgreSQL?
Views in SQL are updatable whereas not in PostgreSQL.
SQL gives computed columns whereas PostgreSQL does not.
Dissimilar to SQL, in PostgreSQL, you don’t require a DLL to see what the code is doing.
SSL connections are used to encrypt server or client transmissions so that security will be assured.
22. Tell the function of the Atomicity property in PostgreSQL?
Atomicity property assures the successful fulfillment of all the operations in a work unit.
23. Tell me the benefits of PostgreSQL?
Some of the benefits of PostgreSQL are open-source DBMS, ACID compliance, community support, full-text search, diverse indexing techniques, diversified extension functions, a variety of replication methods, etc.
24. What does Write-Ahead Logging do?
The Write-Ahead Logging improves database reliability by logging changes before any modifications or updates are made to the database
25. Name some data administration tools supported by PostgreSQL?
Psql, Pgadmin, and Phppgadmin are some data administration tools supported by PostgreSQL.
26. Tell me the way to store the binary data in PostgreSQL?
By using bytes or large object features we can store the binary data in PostgreSQL.
27. Explain the non-clustered index?
The index rows order doesn’t check the order in real data.
28. Tell me the objective of table space in PostgreSQL?
The table space in PostgreSQL is a location in the disk. In this, PostgreSQL stockpiles the data files, which include indices and tables, etc.
29. Tell me the disadvantages of PostgreSQL?
It is more lagging than MySQL on the implementation front.
It doesn’t have the support of a good number of open source applications when compared to MySQL.
Since it concentrates more on compatibility, modifications made to enhance the speed need more work.
30. What is a token representation in a SQL Statement?
A token represents an identifier, quoted identifier, keyword, special character symbol, or a constant.
31. Explain Cube Root Operator (||/) in PostgreSQL?
PostgreSQL Cube Root Operator (||/) helps in getting the cube root of a number.
Example
SELECT ||/40 AS “Cube Root of 40”;
32. How can we modify the datatype of the column in PostgreSQL?
By using the change column type statement with ALTER TABLE command to modify a column type in PostgreSQL.
Example
ALTER TABLE table_name
ALTER COLUMN column_name [SET DATA] TYPE new_data_type;
33. Explain string constants in PostgreSQL?
It is a series of some characters that are seized by single quotes (').
Example
‘This is a string Constant’
34. Explain multi-version control in PostgreSQL?
Multi-version concurrency control or MVCC is utilized to bypass unneeded locking of the database. This eliminates the time lag for the user to log into his database. This feature or time lag happens when some other person is accessing the content. All the activities are kept as a record.
35. Explain Indices of PostgreSQL?
It has inbuilt functions or techniques like GIST Indices, hash table, and B-tree (Binary tree) that users can use to scan the index in a backward way. Users can also describe their indexes of PostgreSQL.
36. Explain tokens in PostgreSQL?
Tokens in PostgreSQL are the construction blocks of any source code. They are known to include many unique character symbols. These can be considered constants, other identifiers, quoted identifiers, and keywords. Identifiers are used to define variable names like columns, tables, etc.
37. Explain table partitioning in PostgreSQL?
It is the method of dividing a large table into smaller pieces. A partitioned table is a logical format utilized to split a large table into smaller pieces is known as partitions.
38. How to start a database server in PostgreSQL?
Before accessing the database, you are required to start the database server. The server code of the database is named Postgres. The Postgres program must know where to locate the data that it is going to use. This is done by using the -D option. Thus, the easiest way to create the server is:
/usr/local/etc/rc.d/010.pgsql.sh start
/usr/local/etc/rc.d/PostgreSQL start
39. Tell me the way to select the first 10 records in PostgreSQL?
Use the LIMIT command to select the first 10 records in PostgreSQL.
Example
select * from users order by name desc LIMIT 0, 10
40. Explain the base directory in PostgreSQL?
Basically, it is a (data_dir/base) folder where all the PostgreSQL data is stored which you have inserted in your databases. It includes all the sub-directories that a database has used in your clusters.
