50+ Database Developer Interview Questions and Answers

Interview questions for Database Developer

• Waterfall model is a linear approach to software development

• Cursor is a database object used to manipulate data row by row

• Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity, while denormalization is the process of intentionally introducing redundancy to improve performance

• SDLC Lifecycle is a process followed by a development team to create a software product

• SQL is used to mana...read more

My unique blend of technical skills, problem-solving abilities, and collaborative mindset sets me apart as a Database Developer.

• Strong proficiency in SQL and database design, demonstrated by optimizing a large-scale database that improved query performance by 30%.

• Experience with multiple database systems, including MySQL, PostgreSQL, and MongoDB, allowing me to choose the best tool for the job.

• A proven track record of working in cross-functional teams, where I facilitated com...read more

To delete duplicate records from a table, we can use the DISTINCT keyword or GROUP BY clause in SQL.

• Use the DISTINCT keyword to select unique records from the table.

• Use the GROUP BY clause to group the records by a specific column and select only the distinct groups.

• Use the HAVING clause to filter out groups with more than one record.

• Create a temporary table with distinct records and then delete the original table and rename the temporary table.

• Use the ROW_NUMBER() function t...read more

Optimize select statements by using indexes, avoiding unnecessary joins, and limiting the number of columns selected.

• Use indexes to speed up queries

• Avoid unnecessary joins and subqueries

• Limit the number of columns selected

• Use WHERE clauses to filter results

• Use GROUP BY and ORDER BY clauses wisely

• Consider using stored procedures or views

• Regularly analyze and optimize the database

Indexing is a technique to improve database performance by reducing the time taken to retrieve data.

• Indexes are created on one or more columns of a table.

• Types of indexes include clustered, non-clustered, unique, and full-text indexes.

• Clustered indexes determine the physical order of data in a table.

• Non-clustered indexes are separate structures that contain a copy of the indexed columns and a pointer to the actual data.

• Unique indexes ensure that each value in the indexed colu...read more

To find people from the same city, use SQL queries to filter records based on the city column in the database table.

• Use a SQL SELECT statement to retrieve records: SELECT * FROM people WHERE city = 'CityName';

• You can group results by city to see counts: SELECT city, COUNT(*) FROM people GROUP BY city;

• To find people from multiple cities, use the IN clause: SELECT * FROM people WHERE city IN ('City1', 'City2');

• Consider indexing the city column for faster query performance if th...read more

Joins are used to combine data from two or more tables based on a related column. A view is a virtual table created from a query.

• Joins are used to retrieve data from multiple tables based on a related column

• There are different types of joins such as inner join, left join, right join, and full outer join

• Views are virtual tables created from a query that can be used to simplify complex queries or restrict access to sensitive data

• Views do not store data themselves, but rather pr...read more

Normalization is a process used to organize a database into tables and columns to reduce redundancy and improve data integrity.

• First Normal Form (1NF) - Eliminates duplicate data by ensuring each column contains atomic values.

• Second Normal Form (2NF) - Requires that each non-key attribute is fully functionally dependent on the primary key.

• Third Normal Form (3NF) - Ensures that non-key attributes are not transitively dependent on the primary key.

• Boyce-Codd Normal Form (BCNF) -...read more

This query generates all possible combinations of matches from a given dataset.

• Use a self-join to pair matches from the same table.

• Example: SELECT a.match_id, b.match_id FROM matches a, matches b WHERE a.match_id < b.match_id;

• This ensures unique combinations without duplicates.

• Consider using GROUP BY or ORDER BY for organized results.

Query to retrieve employees who joined the company within a specific recent timeframe.

• Use the SELECT statement to choose employee details.

• Filter results using the WHERE clause with a date condition.

• Example: SELECT * FROM employees WHERE join_date >= DATEADD(month, -3, GETDATE());

• Adjust the timeframe as needed (e.g., last month, last year).

• Ensure the join_date column is in the correct date format.

Normalization technique is used to organize data in a database to reduce redundancy and improve data integrity.

• Normalization involves breaking down a table into smaller tables and defining relationships between them.

• It helps in reducing data redundancy by storing data in a structured and organized manner.

• Normalization ensures data integrity by minimizing data anomalies such as update, insert, and delete anomalies.

• There are different normal forms such as 1NF, 2NF, 3NF, BCNF, a...read more

I have used various types of indexes such as clustered, non-clustered, unique, and composite indexes in my previous organization.

• Utilized clustered indexes to physically sort the data on disk based on the index key

• Implemented non-clustered indexes to improve query performance by creating a separate data structure

• Employed unique indexes to enforce uniqueness on one or more columns

• Created composite indexes to improve query performance on multiple columns

Yes, I have experience working on Hadoop.

• I have worked on Hadoop for data processing and analysis.

• I am familiar with Hadoop's distributed file system (HDFS) and MapReduce framework.

• I have used Hadoop to handle large volumes of data and perform complex computations.

• I have experience with Hadoop ecosystem tools like Hive, Pig, and Spark.

• I have optimized Hadoop jobs for performance and scalability.

• I have worked on Hadoop clusters and managed data storage and retrieval.

• I have imp...read more

Azure SQL is a managed relational database service while Azure SQL MI is a fully managed, cloud-based version of SQL Server.

• Azure SQL is a Platform as a Service (PaaS) offering, while Azure SQL MI is an Infrastructure as a Service (IaaS) offering.

• Azure SQL is designed for small to medium-sized databases, while Azure SQL MI is designed for larger databases with more complex requirements.

• Azure SQL provides automatic patching and backups, while Azure SQL MI allows more control o...read more

Stored procedures are pre-written SQL codes that can be saved and reused in a database.

• Stored procedures are used to improve database performance and security.

• They can be called from within an application or directly from the database.

• They can accept input parameters and return output parameters or result sets.

• Examples include procedures for inserting, updating, and deleting data.

• They can also be used for complex data manipulation and business logic.

Indexes are data structures that improve the speed of data retrieval in databases.

• Indexes are built on columns in database tables to quickly locate rows based on the indexed column values.

• They are typically implemented using B-tree or hash data structures.

• Examples of indexes include primary keys, unique keys, and non-unique indexes.

• Creating an index involves sorting the values of the indexed column and storing pointers to the corresponding rows.

COALESCE returns the first non-null value from a list of arguments, useful for handling nulls in SQL queries.

• COALESCE takes two or more arguments and returns the first one that is not NULL.

• Example: COALESCE(NULL, 'Hello', 'World') returns 'Hello'.

• It can be used to provide default values: COALESCE(column_name, 'Default Value')

• COALESCE is often used in SELECT statements to avoid null results.

SQL is a programming language used to manage and manipulate relational databases.

• SQL stands for Structured Query Language

• It is used to create, modify, and query databases

• It is used in various industries such as finance, healthcare, and e-commerce

• Examples of SQL-based databases include MySQL, Oracle, and Microsoft SQL Server

Temporary table is a table that exists temporarily and is used to store data temporarily. A view is a virtual table that is based on the result-set of an SQL statement.

• Temporary table is created for a specific session or task and is dropped automatically when the session is closed or the task is completed.

• Temporary table can be used to store intermediate results during complex queries or to store data that needs to be manipulated before being inserted into a permanent table.

• V...read more

DBMS stands for Database Management System. It is a software that allows users to interact with databases.

• DBMS is used to create, update, and manage databases.

• It provides tools for data storage, retrieval, and manipulation.

• Examples of DBMS include MySQL, Oracle Database, and Microsoft SQL Server.

Procedure with bulk collect for array of strings

• Use FORALL statement for efficient processing

• Declare a collection type

• Use LIMIT clause to control memory usage

Drop command removes the entire table while delete command removes specific rows.

• Drop command is a DDL (Data Definition Language) command while delete command is a DML (Data Manipulation Language) command.

• Drop command cannot be rolled back while delete command can be rolled back using transaction.

• Drop command is faster than delete command as it removes the entire table at once.

• Example: DROP TABLE table_name; DELETE FROM table_name WHERE condition;

Yes, a cluster is a group of servers or computers that work together to provide high availability and scalability.

• A cluster is used to distribute the workload and improve performance.

• It provides redundancy and fault tolerance by allowing one server to take over if another fails.

• Clusters can be used in various applications like database systems, web servers, and high-performance computing.

• Examples of cluster technologies include Microsoft SQL Server AlwaysOn, Apache Hadoop, an...read more

Data structure is a way of organizing and storing data in a computer so that it can be accessed and manipulated efficiently.

• Data structure defines the relationship between data elements and the operations that can be performed on them.

• It helps in optimizing the use of memory and improving the efficiency of algorithms.

• Examples of data structures include arrays, linked lists, stacks, queues, trees, and graphs.

The 10 digit number should be formatted as 4_3_3.

• Split the 10 digit number into 3 parts: first 4 digits, next 3 digits, and last 3 digits.

• Insert an underscore (_) between the parts to get the desired format.

• Example: 1234567890 should be formatted as 1234_567_890.

Magic tables are temporary tables created by SQL Server during DML operations.

• Magic tables are used to access the data before and after an INSERT, UPDATE, or DELETE operation.

• They are created automatically by SQL Server and cannot be modified by the user.

• The inserted and deleted tables are examples of magic tables.

• They are useful for auditing and logging changes to a database.

Output parameters are variables used to return values from a function or stored procedure.

• Output parameters are declared with the OUTPUT keyword in SQL Server.

• They can be used to return a single value or a table of values.

• Output parameters are useful for passing data between stored procedures or functions.

• They can also be used to return status codes or error messages.