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DBMS Interview Questions and Answers
1. What is a Database Management System (DBMS)?
The term "Database Management System(DBMS)" refers to a group of programs that enable users to safely save and retrieve data from a database. A DBMS enables you to conduct a variety of actions, including establishing new databases, adding and removing data, and updating existing data. It is a considerably more secure method of storing data than the standard file-based approach. MySQL, Oracle, and SQL Server are all popular examples.
Advantages of DBMS
- Segregation of application program.
- Minimal data duplicity or data redundancy.
- Easy retrieval of data using the Query Language.
- Reduced development time and maintenance needs.
- With Cloud Datacenters, we now have Database Management Systems capable of storing almost infinite data.
- Seamless integration into the application programming languages makes it very easier to add a database to almost any application or website.
2. What Are The Benefits Of a Relational Database Management System Over Conventional File-Based Systems?
Many of the most significant advantages of DBMSs over conventional file-based systems include the following:
- Controlling data redundancy is possible.
- No unauthorized access to data
- Data is easily accessible and processed Provides backup and data recovery
- Data is easily accessible and processed Provides backup and data recovery Multiple user interfaces
- Provides data recovery and backup
3. Define "Normalization" in DBMS.
Database Normalization is a technique of organizing the data in the database. Normalization is a systematic approach of decomposing tables to eliminate data redundancy(repetition) and undesirable characteristics like Insertion, Update and Deletion Anomalies. It is a multi-step process that puts data into tabular form, removing duplicated data from the relation tables.
Normalization is used for mainly two purposes,
- Eliminating redundant(useless) data.
- Ensuring data dependencies make sense i.e data is logically stored.
4. Define Denormalization In Relational Database Management Systems.
Denormalization is the process of enriching a database with duplicate data. It is performed after normalization in order to minimize costly joins. It is a typical database optimization approach that aids in improving a database's performance.
5. Describe The Many Kinds of Database Management System Architectures.
There are three distinct kinds of database management system architectures:
- Single-tier design - 1-tier DBMS architecture also exists, this is when the database is directly available to the user for using it to store data. Generally, such a setup is used for local application development, where programmers communicate directly with the database for quick response.
- Two-tier architecture - 2-tier DBMS architecture includes an Application layer between the user and the DBMS, which is responsible to communicate the user's request to the database management system and then sending the response from the DBMS to the user.
- Three-tier architecture - A layer separates the client and server machines, preventing them from communicating directly. A client database management system application running on the client computer communicates with a server database management system application running on the server machine.
6. What is a Checkpoint In A Relational Database Management System?
A checkpoint or savepoint is used to designate a system state in which all previous logs are deleted. Checkpoints may be used to recover from a system crash. Rather than processing the transactions sequentially, you may utilize checkpoints to get the most recent recorded snapshot of the database.
7. SQL is one of the primary features for doing any kind of execution with data, specifically in DBMS. Explain the exact purpose of utilizing SQL in DBMS.
SQL is basically called the structured query language. One of the primary goals of using the same is to connect with one of the expressly specified relational databases in some form by inserting, deleting, or updating data from the defined database.
8. Define a Data Model.
A data model is a set of tools for describing data, semantics, and constraints. Additionally, they aid in describing the link between data items and their associated properties. The most often used data models are the hierarchical data model, the network data model, the entity-relationship data model, and the relational data model. Additionally, you may review other data modeling interview questions to get additional knowledge about data models.
9. How Are An Entity And An Attribute Different?
An entity is a database term that relates to a physical item in the actual world. For instance, in a personnel database, the various entities may include employees, classifications, and departments.
An attribute is a property that identifies an entity. For instance, the entity "employee" may contain the property's name, ID, and age.
10. Describe the ACID characteristics of a database management system.
ACID characteristics are the fundamental principles of a database management system that must be obeyed in order to maintain data integrity. They are as follows:
- Atomicity - Atomicity is sometimes referred to as the "all or nothing" rule, which states that everything viewed as a single unit is either performed completely or not at all.
- Consistency - This attribute indicates that the database's data is consistent both before and after each transaction.
- Isolation - This attribute specifies that a variable number of concurrent transactions may be conducted.
- Durability - This attribute guarantees that when a transaction is done, it is kept in non-volatile memory.
11. What are you referring to when you say functional dependency?
Functional or database dependency establishes the relationship between two attributes. The symbol X -> Y indicates that Y is functionally reliant on X.
12. What is the primary difference between DELETE and TRUNCATE?
- The DELETE command is used to delete rows from a table based on the WHERE clause criteria. The lost rows may be restored.
- TRUNCATE is used to remove every row from a table without specifying any constraints. The rows are not reversible.
13. Describe the various normal forms used in normalization.
The most often seen normal forms are as follows:
- First Normal Form(1NF)- A table is considered to be in the first normal form (1NF) if it contains only atomic values.
- Second Normal Form (2NF) - A table is said to be in 2NF if it is in 1NF and none of its non-prime characteristics is reliant on any candidate key.
- Third Normal Form (3NF) - A table is said to be in 3NF if it is in 2NF and none of its non-prime characteristics is reliant on any super key.
- Boyce & Codd Normal Form(BCNF) - A table is said to be in BCNF if it is in 3NF and for each functional dependence A->B, B is the table's super key.
14. How are Hash join and Merge join different?
- Hash join - A hash join is a technique for joining huge tables together.
- Merge join - A merge join is used to combine the output streams of two connected tables.
15. Define a Relationship In A Relational Database Management System (RDBMS) And Its Many Forms.
An affiliation or connection between two or more data elements is referred to as a relationship. In a relational database management system, there are three primary kinds of relationships:
- One-to-one - A single record in one table is associated with a single record in another table, and vice versa.
- Many to one - A single entry in one table is connected to numerous entries in other tables, and vice versa.
- Many to many - Numerous records in one table are connected to numerous entries in another table. It only depicts the user's interaction with the database.
DBMS Interview Questions and Answers for Freshers
1. What is the difference between a primary key and a foreign key in a database?
- Primary key: A primary key is a unique identifier for a record in a table. It must be unique and not null. It is used to uniquely identify each record in a table and enforce data integrity.
- Foreign key: A foreign key is a column in a table that refers to the primary key of another table. It establishes a relationship between two tables and ensures referential integrity, meaning that values in the foreign key column must match the values in the primary key column of the referenced table.
2. What is a stored procedure in a database and why is it used?
A stored procedure is a pre-compiled set of SQL statements that are stored in a database and can be executed repeatedly. It is used to encapsulate complex business logic or data processing tasks within the database itself.
Stored procedures can improve performance, reduce network overhead, and provide better security by allowing controlled access to data and operations.
3. What are database indexes and why are they important?
A database index is a data structure that provides a fast and efficient way to look up rows in a table based on the values in one or more columns. Indexes are important for improving query performance, as they allow the database to quickly locate and retrieve data without scanning the entire table.
However, indexes also add overhead in terms of storage space and update performance, so they need to be carefully chosen and maintained to achieve optimal performance.
4. What is a database transaction and what are its properties?
A database transaction is a sequence of one or more operations (such as insert, update, and delete) that are executed as a single unit of work. The properties of a database transaction, known as ACID properties, are:
- Atomicity: Ensures that a transaction is either fully completed or fully rolled back, with no intermediate states.
- Consistency: Ensures that a transaction transforms a database from one consistent state to another, preserving integrity constraints.
- Isolation: Ensures that concurrent transactions are isolated from each other and do not interfere with each other's operations.
- Durability: Ensures that once a transaction is committed, its changes are permanent and survive system failures.
5. What is a database view and why is it used?
A database view is a virtual table that is created by combining data from one or more tables in a database.
It is used to provide a logical or customized view of the data to users or applications, without changing the actual data stored in the tables.
Views can be used to simplify complex queries, encapsulate business logic, and provide an additional layer of security by controlling access to data.
6. What is database indexing and how does it work?
Database indexing is the process of creating data structures, called indexes, that provide a fast and efficient way to look up rows in a table based on the values in one or more columns.
Indexes are organized in a specific data structure, such as a B-tree or a hash table, which allows the database to quickly locate and retrieve data without scanning the entire table.
Indexing can significantly improve query performance but should be used judiciously, as it also adds overhead in terms of storage space and update performance.
7. What is the difference between a candidate key and a foreign key in a database?
In a database, a candidate key is a column or a combination of columns that uniquely identifies a record in a table, just like a primary key.
However, unlike a primary key, a table can have multiple candidate keys. On the other hand, a foreign key is a column or a combination of columns in a table that refers to the primary key of another table.
It establishes a relationship between two tables and is used to maintain referential integrity by enforcing constraints on the relationship between the tables.
8. What is a primary key and why is it important in a relational database?
A primary key is a unique identifier for a record in a relational database table. It ensures that each record in the table is uniquely identifiable and can be used as a reference in relationships with other tables.
Primary keys are crucial for maintaining data integrity, enforcing referential integrity, and allowing efficient and fast data retrieval.
9. What is the difference between a clustered and a non-clustered index in a database?
In a database, a clustered index determines the physical order of data in a table based on the indexed column, while a non-clustered index does not affect the physical order of data.
In other words, with a clustered index, the rows in a table are stored on disk in the same order as the index, whereas with a non-clustered index, the index and the table data are stored separately.
As a result, queries that use a clustered index for data retrieval can be faster, but updates to clustered index columns can be slower compared to non-clustered indexes.
Conclusion
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These questions can make you help to Ace the DBMS interview. All the Best!!
