Here are some common relational database interview questions and general answers, but keep in mind that specific answers may vary depending on the company and the role you are interviewing for:
What is a relational database?
A relational database is a type of database that organizes data into one or more tables, with each table consisting of a set of rows and columns. The tables are related to one another through the use of a key, allowing for easy data retrieval and manipulation.
What is the purpose of a primary key in a relational database?
A primary key is a unique identifier for each row in a table. It is used to enforce the integrity of the data by ensuring that each row has a unique value, and it is also used to establish relationships with other tables through foreign keys.
What is normalization in a relational database?
Normalization is the process of organizing data in a database into separate tables based on their logical relationships. The goal of normalization is to minimize data redundancy and improve data integrity by ensuring that each piece of data is stored in only one place.
What is a join in a relational database?
A join is a query that combines rows from two or more tables based on a related column between them. There are several types of joins, including inner join, left join, and right join.
What is ACID in a relational database?
ACID is an acronym that stands for Atomicity, Consistency, Isolation, Durability. These are the four properties that ensure that database transactions are processed reliably. Atomicity guarantees that a transaction is treated as a single, indivisible operation; consistency ensures that a transaction brings the database from one valid state to another; isolation ensures that concurrent transactions do not interfere with one another; durability guarantees that once a transaction has been committed, it will survive permanently.
How do you handle concurrency in a relational database?
Concurrency can be handled through the use of locking mechanisms, such as pessimistic locking and optimistic locking. Pessimistic locking involves preventing other users from accessing a piece of data while it is being updated, while optimistic locking involves allowing multiple users to access the data at the same time and then handling conflicts that may arise when the data is being updated. Additionally, using a transaction isolation level can also help to control concurrency issues.
What is an index in a relational database?
An index is a data structure that helps to quickly locate and retrieve specific rows in a table. It is typically created on one or more columns and can be used to improve the performance of queries.
What is a view in a relational database?
A view is a virtual table that is based on the result of a SELECT statement. It does not store data itself, but rather provides a way to access data from one or more tables in a specific way.
What is a stored procedure in a relational database?
A stored procedure is a pre-compiled collection of SQL statements that can be executed with a single call. They are useful for encapsulating logic and for improving performance by reducing network traffic and parsing overhead.
What is a trigger in a relational database?
A trigger is a set of instructions that are automatically executed in response to certain events, such as the insertion of a new row or the update of an existing row. They are useful for enforcing business rules and for maintaining data integrity.
How do you backup and restore a relational database?
There are several methods for backing up and restoring a relational database, including full backups, incremental backups, and log backups. The specific method used will depend on the database management system (DBMS) being used and the requirements of the organization. Typically, a backup schedule should be established and test restores should be performed regularly to ensure the backups are working correctly.
How do you monitor and optimize the performance of a relational database?
Performance monitoring and optimization of a relational database involves tracking key performance metrics such as response time, CPU and memory usage, and disk I/O. The database can be optimized by fine-tuning the configuration settings, creating indexes, and optimizing the SQL queries. Additionally, regular maintenance tasks such as index defragmentation, statistics update and table partition can also improve the performance.
What is a data warehouse?
A data warehouse is a large, centralized repository of data that is specifically designed for reporting and data analysis. It is designed to handle large amounts of data from multiple sources and typically uses a different data model than transactional databases.
What is the difference between a clustered index and a non-clustered index?
A clustered index determines the physical order of data in a table, while a non-clustered index creates a separate object that contains the indexed data along with a pointer to the actual data row. A table can have only one clustered index, but multiple non-clustered indexes.
What are some of the advantages and disadvantages of using a NoSQL database?
Advantages of NoSQL databases include their ability to handle large amounts of unstructured data, their horizontal scalability, and their ability to handle high write loads. Disadvantages include the lack of support for complex transactions, the lack of support for advanced query languages, and the lack of support for referential integrity.
What is the difference between a subquery and a join?
A subquery is a query nested within another query that is used to filter the results of the outer query. A join is a query that combines rows from two or more tables based on a related column between them.
How would you design a database schema for a social media application?
Designing a database schema for a social media application would involve creating tables for users, posts, comments, likes, and friends. The user table would contain information about the user, such as their name and email address. The posts table would contain information about each post, such as the post text and the user who created it. The comments, likes, and friends tables would contain information about comments, likes, and friend connections between users, respectively. The relationships between these tables would be established through the use of primary and foreign keys.
What is a transaction in a relational database?
A transaction is a unit of work that is executed against a relational database management system (RDBMS). A transaction is a sequence of one or more SQL statements that are executed as a single unit of work. The main goal of a transaction is to maintain the integrity of the data by ensuring that all the statements within the transaction are executed successfully or none of them are executed at all.
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- Document Database Vs. Key Value Store
- Document Database Vs. Relational Database
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