40+ 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

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

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

• Indexes are data structures that store a small portion of the table data in an optimized format for quick retrieval.

• They help in speeding up data retrieval operations such as SELECT queries by reducing the number of rows that need to be scanned.

• Indexes can be created on one or more columns of a table to improve the performance of queries that filter or sort by those columns.

• Examples o...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

To run parallel queries for multiple databases, use parallel processing techniques and tools.

• Use parallel processing techniques such as multi-threading or distributed computing to run queries simultaneously on multiple databases.

• Consider using tools like Apache Hadoop or Apache Spark for parallel processing of queries across multiple databases.

• Ensure proper resource allocation and optimization to prevent performance issues when running parallel queries on multiple databases.

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

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.

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.

Different types of joins are used to combine rows from two or more tables based on a related column between them.

• Inner Join: Returns rows when there is at least one match in both tables.

• Left Join (or Left Outer Join): Returns all rows from the left table and the matched rows from the right table.

• Right Join (or Right Outer Join): Returns all rows from the right table and the matched rows from the left table.

• Full Join (or Full Outer Join): Returns rows when there is a match in ...read more

A recursive CTE is a Common Table Expression that references itself.

• It is used to perform recursive operations on hierarchical data.

• It consists of two parts: the anchor member and the recursive member.

• The anchor member is the base case and the recursive member is the recursive case.

• It can be used to traverse a tree structure or to calculate running totals.

• It can improve performance and simplify complex queries.

Database architecture refers to the design and structure of a database system.

• Database architecture includes the organization of data, storage, retrieval, and security mechanisms.

• It involves defining the relationships between data elements and how they are stored and accessed.

• Examples of database architectures include hierarchical, network, relational, and object-oriented.

• Database architecture also includes the choice of database management system (DBMS) and hardware infrastr...read more

Left join includes all records from the left table and matching records from the right table. Right join includes all records from the right table and matching records from the left table.

• Left join: Returns all records from the left table and the matched records from the right table.

• Right join: Returns all records from the right table and the matched records from the left table.

• Example: Left join - SELECT * FROM table1 LEFT JOIN table2 ON table1.id = table2.id;

• Example: Right ...read more

Query to find the total sales amount for each product category

• Use GROUP BY clause to group the sales by product category

• Use SUM function to calculate the total sales amount

• Join the sales table with the product table to get the product category

Temp tables are used to store intermediate results during query processing.

• Temp tables are created in tempdb database.

• They can be local or global.

• Local temp tables are only visible to the current session.

• Global temp tables are visible to all sessions.

• They can be created using SELECT INTO or CREATE TABLE statements.

• They can be used to store intermediate results during complex queries.

• They are automatically dropped when the session that created them ends.

• They can also be explic...read more

PostgreSQL is open-source, highly extensible, and has strong support for advanced features.

• PostgreSQL is open-source, while Oracle is a proprietary database system.

• PostgreSQL has strong support for advanced features like JSON data types, full-text search, and custom extensions.

• PostgreSQL is highly extensible, allowing users to create custom functions, data types, and indexing methods.

• PostgreSQL has a strong community support and regular updates, making it a popular choice for...read more

Abstract is a concept or idea that is not concrete or tangible.

• Abstract refers to something that is theoretical or conceptual rather than physical.

• It is often used in programming to define classes or methods that cannot be instantiated.

• Abstract art does not attempt to represent an accurate depiction of visual reality.

Inheritance is a concept in object-oriented programming where a class can inherit attributes and methods from another class.

• Allows for code reusability and promotes a hierarchical structure

• Derived classes can access and modify the properties and behaviors of the base class

• Types of inheritance include single, multiple, multilevel, and hierarchical inheritance

Different types of joins in SQL can lead to performance issues and incorrect results if not used properly.

• Inner join: Returns only the rows that have matching values in both tables.

• Outer join: Returns all rows from both tables, filling in NULL values for unmatched rows.

• Cross join: Returns the Cartesian product of the two tables, potentially leading to a large result set.

• Self join: Joins a table to itself, useful for comparing rows within the same table.

Delete removes rows one by one, while truncate removes all rows at once.

• Delete is a DML command, while truncate is a DDL command.

• Delete can be rolled back, while truncate cannot be rolled back.

• Delete fires triggers, while truncate does not fire triggers.

• Delete is slower as it logs individual row deletions, while truncate is faster as it logs the deallocation of the data pages.

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

A database is a structured collection of data that is organized in a way that allows for easy access, management, and retrieval.

• A database stores data in tables, which consist of rows and columns.

• It allows for efficient querying and manipulation of data.

• Examples of databases include MySQL, Oracle, and MongoDB.

PM key is a primary key in a database table that uniquely identifies each record.

• PM key stands for Primary Key

• It is used to uniquely identify each record in a database table

• It ensures data integrity and helps in efficient data retrieval

• Example: In a table of employees, the PM key could be the employee ID

DDL is used to create, modify or delete database objects while DML is used to manipulate data within those objects.

• DDL stands for Data Definition Language

• DML stands for Data Manipulation Language

• DDL is used to create, modify or delete database objects like tables, indexes, etc.

• DML is used to manipulate data within those objects like inserting, updating, deleting data

• Examples of DDL statements are CREATE, ALTER, DROP

• Examples of DML statements are INSERT, UPDATE, DELETE

Index is a data structure that improves the speed of data retrieval in a database.

• Indexes are used to quickly locate data without having to search every row in a database table.

• They can be created on one or more columns in a table.

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

• Examples of indexes are primary keys, foreign keys, and indexes created for frequently searched columns.

Stored procedures are used to perform a set of actions, while functions return a single value.

• Stored procedures can perform multiple actions and can return multiple result sets.

• Functions are used to return a single value based on input parameters.

• Stored procedures can be called independently, while functions are typically called within SQL statements.

• Stored procedures can contain DML statements, while functions cannot.

File groups are logical containers for database files that can be used to manage storage and backup operations.

• File groups allow for the organization of database files into logical units.

• They can be used to manage storage and backup operations.

• A database can have multiple file groups, each with its own set of files.

• File groups can be used to control the placement of data and indexes on different physical disks.

• File groups can also be used to control the backup and restore ope...read more

Constraints in SQL are rules that are enforced on data in a table to maintain data integrity.

• Constraints ensure data accuracy and consistency in a database.

• Common constraints include NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK constraints.

• Example: CREATE TABLE Students (ID INT PRIMARY KEY, Name VARCHAR(50) NOT NULL, Age INT CHECK (Age >= 18));

MERGE is a SQL command used to combine INSERT, UPDATE, and DELETE operations into a single statement.

• MERGE is used to synchronize two tables by inserting, updating, or deleting rows based on a specified condition.

• It is useful for data warehousing and ETL processes.

• MERGE can improve performance by reducing the number of round trips between the client and server.

• Syntax: MERGE INTO target_table USING source_table ON condition WHEN MATCHED THEN UPDATE SET column1 = value1, column...read more

Writing SQL queries to retrieve data from a database

• Use SELECT statement to retrieve data from tables

• Use WHERE clause to filter results based on specific conditions

• Use JOIN clause to combine data from multiple tables