PostgreSQL Interview Questions and Answers
Intermediate / 1 to 5 years experienced level questions & answers
Ques 1. What is PostgreSQL, and how does it differ from other relational database systems?
PostgreSQL is an open-source relational database management system (RDBMS). It differs from others by its extensibility and support for SQL and procedural languages.
Ques 2. Describe the role of the PRIMARY KEY constraint in PostgreSQL.
The PRIMARY KEY constraint uniquely identifies each record in a table and ensures data integrity.
Ques 3. Explain the difference between INNER JOIN and LEFT JOIN in PostgreSQL.
INNER JOIN retrieves rows where there is a match in both tables, while LEFT JOIN retrieves all rows from the left table and matching rows from the right table.
Ques 4. What is a subquery, and how is it different from a JOIN?
A subquery is a query nested within another query, returning a single value or a set of values. JOIN combines rows from two or more tables based on a related column.
Ques 5. Explain the purpose of the EXPLAIN command in PostgreSQL.
The EXPLAIN command shows the execution plan of a statement, helping to optimize queries by revealing how PostgreSQL processes them.
Ques 6. What is a view in PostgreSQL, and how is it different from a table?
A view is a virtual table based on the result of a SELECT query. It does not store the data itself but provides a way to represent data stored in one or more tables. Unlike a table, a view does not store data physically.
Ques 7. What are common indexing techniques in PostgreSQL, and when should they be used?
Common indexing techniques include B-tree, Hash, and GiST indexes. They should be used to improve query performance, especially for columns frequently used in WHERE clauses or JOIN conditions.
Ques 8. Explain the difference between VACUUM and ANALYZE in PostgreSQL.
VACUUM is used to reclaim storage occupied by dead tuples, while ANALYZE is used to update statistics about the distribution of data in a table, helping the query planner make better decisions.
Ques 9. What is the purpose of the pg_hba.conf file in PostgreSQL?
The pg_hba.conf file controls client authentication, specifying which hosts are allowed to connect to the PostgreSQL server and how they can authenticate.
Ques 10. Explain the concept of normalization in the context of database design.
Normalization is the process of organizing data to eliminate redundancy and dependency, ensuring data integrity and reducing the likelihood of anomalies in a database.
Ques 11. Explain the difference between a stored procedure and a function in PostgreSQL.
Stored procedures are precompiled sets of one or more SQL statements stored in the database, while functions return a value and can be used in SQL queries like any other value.
Ques 12. What is the purpose of the COPY command in PostgreSQL?
The COPY command is used to copy data between a file and a table or between tables. It is a high-performance mechanism for bulk data loading.
Ques 13. What is a materialized view in PostgreSQL, and when should it be used?
A materialized view is a snapshot of a query result that is stored and can be queried like a table. It should be used when you need to precompute and store the results of a complex query for faster retrieval.
Ques 14. Explain the difference between a hot standby and a warm standby in PostgreSQL replication.
A hot standby is a replica that is actively applying changes from the primary server and is ready for failover. A warm standby is a replica that is not actively applying changes but can quickly take over in case of a primary failure.
Ques 15. What is the purpose of the pg_stat_bgwriter view in PostgreSQL?
The pg_stat_bgwriter view provides statistics about the background writer process in PostgreSQL, helping monitor and optimize the writing of dirty buffers to disk.
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