Interview Questions.

DBMS Interview Questions and Answers - Sep 08, 2021


DBMS Interview Questions and Answers

A database is the spine of any IT gadget. As a Database Developer, I am sure you'll want to prove your knowledge and knowledge to your subsequent process interview and win a function. Here is the list of top 50 DBMS Interview questions to help you sail through. In addition, to beautify your abilties you may go through SQL Tutorials and Top SQL Interview Questions as SQL is an integrated and a critical function in a DBMS (Database Management System).

DBMS Interview Questions and Answers

Question: Define a DBMS (Database Management System) and what's it used for?

Answer: DBMS are software packages that help you build and hold logically associated records also referred to as the database. Here are a few blessings of using a DBMS:

Data Redundancy is controlled.

Unauthorized get admission to is confined.

Enforces integrity constraints.

Data availability and sharing

Data safety and garage

Question: What is a Database?

Answer: The database is a group of ordered information, ordered and stored electronically. Such organized statistics can be without problems accessed, aggregated and managed. The database is managed and monitored through a Database Management System or DBMS.

Question: How might you outline a DBMS checkpoint?

Answer: A checkpoint is a factor earlier than which all the transactions within the DBMS had been dedicated, and the database turned into in a consistent country. It is a point whilst a backup is taken, and all the dirty pages (in-memory changed pages) and antique transaction logs are cleared from the gadget to launch reminiscence area and saved completely into a garage disk. For instance, a manual checkpoint may be introduced as follows:


in which 10 is the duration in seconds.

Read extra.

Question: Explain the different database languages sorts.

Answer: There are 4 types:

DDL (Data Definition Language): is used to outline the database structure or skeleton, as an example, growing the schema, tables, indexes, constraints etc. Some DDL statements are created, modify, drop, rename, truncate, comment.

DCL (Data Control Language): used to retrieve the saved facts. Permissions and get entry to manage come beneath DCL and are performed the usage of the furnish and revoke commands.

DML (Data Manipulation Language): Used for having access to and manipulating records. Some DML statements are select, insert, delete, replace, lock desk, explain plan etc. Basically, DML statements manage consumer requests.

TCL (Transaction Control Language): used to save or rollback modifications accomplished through DML. The instructions used for TCL are dedicate and rollback.

Question: Do you suspect there are any drawbacks of file processing systems?

Answer: There are numerous risks of report processing structures:

Data redundancy and inconsistency.

Accessing records isn't always efficient or clean.

Data might be saved in specific codecs and as a result difficult to proportion.

Issues with concurrent get right of entry to.

Question: What is supposed through DBMS information abstraction?

Answer: Data abstraction is the hiding of irrelevant facts from the person in order that the interactions with users can be clean. There are three stages of abstraction:

Physical Level: It is the bottom degree of abstraction and tells how facts is bodily stored in reminiscence. Data can be accessed thru sequential or random get entry to. Files are prepared using B+ trees and hashing techniques.

Logical Level: This stage shops statistics in the shape of tables. The relationships between diverse entities are also saved as easy structures.

View Level: ‘View degree’ is the pinnacle-maximum extent of abstraction. Users can view simplest part of the real database, inside the shape of rows and columns. It is possible to have a couple of perspectives of the equal database. Storage and implementation info are hidden from the customers.

Question: Explain what you know about Functional Dependency?

A useful dependency expresses dating between the non-key attributes and the primary key of a table. A practical dependency is of two types – trivial and non-trivial. The courting may be described as A -> B where A is the determinant, and B is the based column.

Question: What is Denormalization?

Answer: It is a way for database optimization in which redundant data is delivered to at least one or more tables to avoid joins. This makes retrieval of statistics faster and extra green and less difficult queries.

Question: Explain the difference among extension and intension?

Answer: Intention is the steady fee, i.E. The description of the database or the schema, which is not likely to change often and is precise for the duration of the database layout segment. The extension is the actual records at a specific time, also known as the database photograph. It is in all likelihood to trade frequently.

Question: What is System R?

Answer: System R is a database management gadget that gives a excessive degree of statistics independence and abstraction of the database from the users. It has statistics manipulate functions like brought on transactions, authorization, integrity assertions and provisions for records consistency.

Question: Explain about the normal bureaucracy BCNF, 1NF, 2NF and 3NF.

Answer: All the above are everyday varieties of information, i.E. Organizing data in this sort of way as to avoid facts redundancy and insert, delete & update anomalies.

1NF: also called the First Normal Form. This rule states that a column of a table can keep simplest atomic (single) fee.

2NF: is brief for 2nd everyday shape. To follow the rule of thumb of 2NF, a desk need to be in 1NF. The rule states that any non-prime characteristic (i.E. Attribute that is not a part of any candidate key) must not be dependent on the proper subset of the desk’s candidate key.

3NF: or 0.33 regular shape, the table must already be in 2NF. The rule states that any transitive dependency (purposeful) of a “non-high” feature on a remarkable key need to be removed.

BCNF: is an advanced and stricter model of 3NF. It is likewise more popularly called three.5NF. For BCNF, a desk have to be in 3NF and comply with the rule of thumb that for any functional dependency A->B, A must be the tremendous key of the desk.

Question: What are ACID residences?

Answer: ACID properties are for transactions:

A => Atomicity: the whole transaction takes place in one pass

C => Consistency: database must be consistent before and after the transaction

I => Isolation: transactions do no longer interfere with each different; more than one

transactions can manifest simultaneously

D => Durability: A successful transaction is pondered even supposing a gadget failure occurs.

Question: Explain the Difference between a DELETE command and TRUNCATE command?


DML type DDL type
Supports WHERE Condition Doesn’t support WHERE condition
Can acquire a row lock Locks the entire table and page
Speed of execution is less It is faster than delete
There is a log for each row A single log that indicates deallocation of a page
Example: DELETE FROM employee WHERE emp_id = 2012; Example: TRUNCATE TABLE employee_temp

Answer: In DBMS, 2-Tier structure is a form of database architecture where the UI or view layer (also known as the presentation) runs on a customer gadget (laptop, pc, pill, cellphone, and so on.) and the facts is saved on a server. To name the database, customers use the ODBC connectivity APIs. This structure enhances the safety of the database, as the consumer can’t access the database at once.

Question: Explain the exclusive styles of database keys?

Answer: There are several sorts of DBMS keys:

Primary Key: column or set of columns that become aware of a particular row in a table.

Super Key: single key or set of more than one keys that identifies rows of a desk.

Candidate Key: A set of attributes which become aware of tuples of a desk uniquely. It is essentially a notable key with out repeated attributes.

Alternate Key: One or greater columns of a table that collectively identify every of a desk uniquely.

Foreign Key: A commonplace column that defines the connection among  tables. Maintains records integrity.

Compound Key: Consists of  extra attributes that uniquely identify a record, even when the column is not unique with the aid of itself

Composite Key: Primary key that has two or more attributes like customer_id + mobile_number

Surrogate Key: Created whilst there's no naturally available primary key for a desk. Presents a completely unique identity to a row inside the desk.

Question: Explain the purpose of normalization in DBMS?

Answer: Normalization is an critical method that eliminates redundancy from a set of relations. It can lessen the irregularities in the insert, delete and replace by dividing massive tables into smaller tables and use keys to link them.

Question: How is the Entity, Entity Type, and Entity Set extraordinary from every other in DBMS?


Entity: An entity is an object with bodily life that is independent and may be differentiated with other objects: instance, an employee, student, path, job and so forth.

Entity type: may be stated as the gathering of comparable entities.

Entity set: Entity set is a mixture of entities of one kind at any factor in time.

Question: What is a CLAUSE in phrases of SQL?

Answer: CLAUSE is an optionally available statement in SQL that defines a situation to present statistics. For example,

select * from employee WHERE emp_id = 2012;

right here, WHERE is the clause that identifies the row to be acquired. Some other clauses in SQL are – GROUP BY, HAVING, ORDER BY

Question: Differentiate between aggregation and atomicity?

Answer: Atomicity manner that each one the actions are achieved without delay, or none is accomplished. This method that if a transaction is incomplete or fails in between everything could be rolled returned to a preceding solid country. We use aggregation to explicit relationships between numerous entities.

Question: What are the special kinds of relationships in the DBMS

Answer: There are three styles of relationships in DBMS:

One-to-One: Each desk document is related to handiest one document in any other table. Example, employee_id, and unique_ssn_id

One-to-many or vice-versa (many-to-one): A document in one table may be associated with a couple of file in some other table. Example, employee_id and phone_number

Many-to-Many: A report in the first table may be related to a couple of statistics within the second table, and vice-versa: example, customer_id and product_id.

Question: Explain correlated subqueries in DBMS?

Answer: Correlated subqueries are subqueries which can be carried out as soon as for every row processed by its principal declaration. For example,

select student_id, student_name, marks from students outer where salary > (select avg(marks) from students where subject = outer.students);

Question: Difference between  and three-tier architectures?

Answer: The two-tier structure follows a consumer-server architecture. There is a immediately communique hyperlink between patron and server. Two-tier architecture gives excessive overall performance as there is no center layer. The client may be any tool like cellular, laptop, computer etc. While all the records sits in a database.

Three-tier structure includes:

Presentation layer: A web browser, java applet, WAP phone and so on.,

A enterprise layer: Business good judgment like facts validation, insertions, calculations, and

A records get right of entry to layer: This is a information source like database, mainframe system or ERP device. The enterprise layer acts as a middle tier that separates the enterprise logic from the presentation and statistics layer for better reusability, statistics integrity, scalability and overall performance.

Question: Differentiate among Trigger and Stored Procedures

Answer: Stored approaches can be invoked explicitly through the consumer. It can take positive input parameters and might return output values. It is similar to every other software. Triggers are known as spontaneously (on its own) while a specific event happens. Triggers can’t take any input values nor return any output values.

Question: What is the distinction among Hash be part of, Merge be a part of and Nested loops?


Hash-join: In this form of be part of, the database does full scanning of the primary desk, builds a RAM hash desk, and then searches for matching tables in the different table. Hash be part of is faster than the nested loop join however consumes more RAM resources.

Merge join: This join makes use of easy concatenation observed via sorting (getting rid of duplicates) and is the simplest approach out of all of the joins.

Nested loop join: In this sort of test, the driving table (predominant) accesses rows via index range scan, and the result set of the riding desk is nested with the probe of the other (secondary) desk the use of the index scan approach itself.

Question: Give the difference between Proactive, Retroactive and Simultaneous Update?


Proactive updates are those that eventuate within the database before they emerge as beneficial within the real-international.

Retroactive updates come approximately after they come to be effective within the actual-global.

Simultaneous updates arise on the identical time as they come to be powerful within the actual-international.

Question: Differences between the clustered and non-clustered index.


Clustered Index Non-clustered Index
Defines the order of physical data storage even if they are inserted in random order. Does not sort the physical data. Indexes are stored in a different place than the actual data
Only one clustered index per table as data can be sorted in a single way only More than one non-clustered index in a table is possible
In many databases, primary key constraint creates a clustered index on the same column. A non-clustered index can be created as: CREATE NON-CLUSTERED INDEX IX_tblStudent_deptt ON student(deptt ASC)
Example, if there is a table student that has a primary key student_id, the data will be stored in ascending order of student_id like 1,2,3,4. The clustered index will be automatically created on student_id. An index is stored in a separate table along with its address (a reference to the row), dept row address ECE <address>
No extra space required for these indexes. Consumes storage space.

No extra space required for these indexes.    Consumes storage area.

Question: Difference among specialization and generalization?


Generalization Specialization
Creating groupings from various entity sets is called generalization Creating subgrouping within an entity set is called specialization
The process starts with several entity sets and creates a high-level entity with some common features Starts with a single entity set and then creates a different set using different features.
Applied to a group of entities Applied to a single entity
Follows bottom-up approach Follows top-down approach

Question: Explain the differences among community and hierarchical database version?


Hierarchical model Network model
Relationship between records is parent-child The relationship is in the form of pointers or links
During update and delete operations, inconsistencies in data may happen No data inconsistencies
Doesn’t support many to many relationships Supports many to many relationships
Creates a tree structure and data traversal is a bit complex Creates graph structure where data traversal is easy as a node can be accessed both ways, i.e. parent-child or vice-versa

Question: What is impasse?

Answer: Deadlock occurs while a hard and fast of strategies are blocked. Each method is preserving up a resource that the other system calls for. The different technique is anticipating a aid to be launched by the equal or every other system. Deadlock can be depicted as:

Question: What is a Hierarchical database Model?

Answer: In a hierarchical database version, facts is prepared into nodes in a tree-like structure. A node is hooked up to simplest one determine node above it. Hence information in this version has a one-to-many relationship. An instance of this version is the Document Object Model (DOM) often used in net browsers.

Question: What is a Network Model?

Answer: The community database model is a polished model of a hierarchical model. Here too, facts is organized in a tree-like structure. However, one baby node may be related to more than one figure nodes. This offers upward push to a many-to-many courting among records nodes. IDMS (Integrated Database Management System), Integrated Data Store (IDS) are examples of Network Databases.

Question: What is an RDBMS?

Answer: A relational database is prepared into tables, statistics, and column and there may be a well-defined dating among database tables. A relational database control machine (RDBMS) is an application that lets in you to create, update, and administer a relational database. Tables communicate and proportion the statistics which permits facts search, statistics company, and reporting. An RDBMS is a subset of a DBMS.

Question: What is an Object-Oriented Database Model?

Answer: In an object-oriented database model, statistics is represented by items. For instance, a multimedia record or record in a relational database is stored as a statistics item instead of an alphanumeric price.

Question: What is SQL?

Answer: SQL (Structured Query Language) is a programming language used to speak with facts stored in databases. SQL language is surprisingly smooth to write down, examine, and interpret.

Question: What are DDL, DML and DCL statements in SQL?


DDL: The Data Definition Language is used to define the database and schema structure by using the usage of a hard and fast of SQL Queries like CREATE, ALTER, TRUNCATE, DROP and RENAME.

DCL: The Data Control Language is used to govern the get entry to of the users to the database through the use of a fixed of commands like GRANT and REVOKE inside the SQL Query.

DML: The Data Manipulation Language is used for retaining the statistics by using the use of SQL queries like SELECT, INSERT, DELETE and UPDATE.

Click right here to recognize extra about SQL Command.

Question: What do you mean by means of Index hunting?

Answer: A database index is a data structure that improves the velocity of statistics retrieval operations on a database. The technique of boosting the gathering of indexes is known as as Index looking. It is achieved via the usage of techniques like query optimization and question distribution.

Question: What is a disbursed database?

Answer: A allotted database is a collection of more than one interconnected databases which are unfold bodily across various places. The databases may be at the identical network or on more than one networks. A DDBMS (Distributed – DBMS) integrates statistics logically in an effort to the consumer it seems as one single database.

Question: What is a database partitioning?

Answer: Database partitioning is a technique wherein a logical database is split into awesome impartial components. The database gadgets like tables, indexes are subdivided and controlled and accessed on the granular degree.

Question: Explain the significance of database partitioning?

Answer: Partitioning is a powerful functionality that increases performance with reduced price. It enhances manageability and improves the availability of data.

Question: What is a static SQL?

Answer: In a static SQL, the SQL statements are embedded or difficult-coded within the utility and that they do no longer trade at runtime. How information is to be accessed is predetermined subsequently it is extra fast and green. The SQL statements are compiled at collect time

Question: What is dynamic SQL?

Answer: In a dynamic SQL, SQL statements are built at runtime, for example, the software can permit the person to create the queries. Basically, you may build your question at runtime. It is relatively slower than the static SQL because the question is compiled at runtime.

Question: Define Data Warehousing.

Answer: Data Warehousing is a technique that aggregates a large amount of records from one or greater assets. Data evaluation is achieved at the statistics to make strategic business decisions for companies.

Question: Name one open-source RDBMS.

Answer: MySQL is an open-source relational database management system, which stores information in tables and maintains a relationship between the facts. It uses the maximum powerful query language SQL (Structured Query Language) for database get right of entry to and has a completely powerful syntax to create simple and complicated queries to retrieve and shape facts. Data in MySQL is prepared and conforms to a positive format, and subsequently it's far the maximum famous established database nowadays. Its ‘loose’ source code is available for have a look at, amendment, and distribution.

Question: What is MongoDB?

Answer: MongoDB is a non-relational unstructured open-supply database. This report-orientated database shops your statistics in collections constituted of person documents. In MongoDB, a document is a huge JSON item with no unique layout or schema. MongoDB represents JSON files in a binary-encoded layout named as BSON

Read the difference between MongoDB vs MySQL

Question: What is BI (Business Intelligence)?

Answer: Business intelligence (BI) is a generation-driven technique for reading information and offering facts to help executives, managers, and other corporate end-customers make commercial enterprise selections. There are many tools available like SAP Business Intelligence, MicroStrategy, Sisense and so forth. The tools are consumer-friendly that facilitates you gather facts from numerous assets for evaluation.

Question: What is the function of a DBA in DBMS?

Answer: The Database Administrator (DBA) plays some crucial roles in an organisation. They are as follows:

Installing and configuring databases

Performance Monitoring

Security making plans and implementation

Data backup and recovery


Data migration

Question: What is an ER diagram in DBMS?

Answer: An entity-relationship version or an entity-relationship diagram is a visible representation of records that's represented as entities, attributes and relationships are set between entities.

Question: What is an Entity in an ER diagram?

Answer: An entity may be a real-world object, which can be effortlessly identifiable. For example, in a library database, books, publishers and members may be considered entities. All those entities have a few attributes or homes that deliver them their identification. In an ER version, the entities are associated with every different.

Question: What is Data Mining?

Answer: Data mining is a technique of sorting through a big amount of information to become aware of styles and trends. It makes use of complicated mathematical and statistical algorithms to section facts for the prediction of probably outcomes. There are many tools for Data Mining like RapidMiner, Orange, Weka and so forth.

Question: What is meant by question optimization?

Answer: Query optimization is an vital feature with regards to the performance of a database. Identifying an green execution plan for comparing and executing a query that has the least envisioned cost and time is known as question optimization.

Question: What is a Catalog?

Answer: A catalog is a table that consists of the records together with the shape of each document, the sort, and garage layout of each statistics object and numerous constraints on the statistics. The records saved in the catalog is known as Metadata.

Question: How many sorts of relationship exist in database designing?

Answer: There are 3 essential relationship models in database layout:-

One-to-one – A row in one table (A) is related to handiest one row in every other table (B)

One-to-many – A row in a table (A) is related to many rows in any other desk (B). But a row in desk (B) is connected to most effective one row in table (A).

Many-to-many – A row inside the table (A) is linked to many rows within the desk (B) and vice-versa

Question: What are the primitive operations not unusual to all database management structures?

Answer: Addition, deletion, and change are the most important primitive operations common to all DBMS.

Question: What is cardinality in context to a database?

Answer: In SQL (Structured Query Language), the term cardinality refers to the individuality of records values contained in a specific column (attribute) of a database table. The lower the cardinality, the extra are the duplicated values in a column.

Question: What is SQL SERVER?

Answer: SQL Server is an RDBMS advanced by using Microsoft. It may be very stable and strong subsequently famous. The latest model of SQL Server is SQL Server 2017.

Question: Under what situations must we use indexes?

Answer: Indexes can be created to implement uniqueness, to facilitate sorting, and to enable rapid retrieval by means of column values. When a column is frequently used it is a superb candidate for an index to be used with suitable conditions in WHERE clauses.

Question: What is a hashing approach in a database?

Answer: Hashing is the transformation of a string of characters into a generally shorter constant-length cost or key that represents the unique string. Hashing is used to index and retrieve items in a database due to the fact it's far faster to locate the item using the shorter hashed key than to locate it the use of the unique cost.

Question: Describe concurrency control?

Answer: Concurrency control is the procedure of coping with simultaneous operations on a database in order that database integrity isn't compromised. There are  tactics to concurrency manipulate.

They are Locking (controlling get admission to to statistics gadgets the usage of locks) and Versioning (using Multi-Version Concurrency Control) respectively.


So, all the very high-quality! Do allow us to know the DBMS questions you confronted within the interview that aren't covered right here in this newsletter so that we can add the ones here for the gain of the DBMS network.

So this sums up the first-rate interview questions, to be able to assist you crack a DBMS Interview. If you desire to cowl extra DBMS interview questions, deliver this brilliant direction a shot. 2 hundred+ SQL interview Questions.

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