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Top 50 DBMS Interview Questions and Answers



Learn: In this article, we are going to discuss about the top 50 DBMS interview questions and answers.
Submitted by Prerana Jain, on June 08, 2018

1) What are the drawbacks of the file system which is overcome on the database management system?

Ans: Data redundancy & isolation, difficulty in accessing data, data isolation, and integrity problem these are drawbacks of the file system.


2) What is database system?

Ans: The database which is the collection of information and DBMS software together is called database system.


3) Which level of abstraction describes what data are stored in the database?

Ans: Logical level describes what data are stored in the database.


4) What is view level or external level data hiding?

Ans: It is the highest level of abstraction that describes only part of the entire database this part implies the interaction of users with the system.


5) Why is the entity set called weak entity set?

Ans: The entity set is called weak entity set because it does not have the primary key.


6) What are the extended features of ER diagram?

Ans: Specialization, generalization, aggregation are the extended features of ER diagram.


7) How many types of relationship exist in database designing?

Ans: There are three major relationship models,

  1. One- to- one
  2. One- to- many
  3. Many- to- many

8) What is the minimum cardinality of zero specifies?

Ans: Partial participation is the minimum cardinality of zero specifies.


9) When the fan trap may exist in ER model.

Ans: When two or more one to more relationships fan out from the same entity set then the fan trap may exist in ER model.


10) What is RAT axioms in DBMS?

Reflexivity, argumentation, transitivity these are the Armstrong rule which is sufficient enough to find closure set.


11) What are database languages?

Ans: These are the special purpose languages in DBMS. It is of three types of DDL (data definition language), DML (data manipulation language, a query language.


12) What is meant by index cardinality?

Ans: Index cardinality is the total number of distinct key values for each index.


13) What is the foreign key?

The attribute of one table which is referencing the primary key of other table is called foreign key.


14) What is prime attribute of the relational schema?

Ans: An attribute is called prime attribute when it is the part of any candidate key in the relational schema.


15) How many types of normal form in normalization?

There are mainly four types of normal form,

  1. 1 NF (first normal form)
  2. 2 NF (second normal form)
  3. 3 NF (third normal form)
  4. BCNF (Boyee-Codd normal form)



16) What is the full form of PGNF?

The full form of PGNF has projected join normal form it is the 5 the normal form and it cannot have a lossless decomposition into any number of smaller tables.

17) What is RDBMS?

Relational database management system (RDBMS) is the database management system that maintains data records and indices in tables


18) What is chasm trap?

Ans: When the two relations are interconnected through partial participation by another relation then it is called chasm trap.


19) What is a transaction in DBMS?

Ans: A transaction is a logical unit of database processing that includes one or more database access operations.


20) Which property makes transaction consistent?

Ans: The transaction should possess several properties called ACID property,

  1. A- Atomicity
  2. C – Consistency
  3. I – isolation
  4. D – Durability

21) What are the different phases of the transaction?

Ans: There are three different phases of the transaction. Analysis phase, Redo phase, Undo phase.


22) What are the Transaction states?

Ans: A transaction moves from one state to the other as it entries the system to be executed. There are many states like active, partially committed, failed, Aborted, committed.


23) What is concurrency?

Ans: Concurrency is the ability of the database system to handle simultaneously a number of transactions by overlapping or interleaving parts of their actions.


24) What is the common problem that happens due to concurrency?

Ans: There are many common problems,

  • Dirty read problem
  • Loss update problem
  • Unrepeatable read problem
  • Phantom read problem

25) What is read timestamp?

Ans: It is the timestamp of the transaction that has performed latest read operations.




26) What is SQL?

Ans: SQL stands for (structured query language). It is a standard computer language for accessing and manipulating database systems. It is also used to retrieve and update data in a database.


27) What is scheduling?

Ans: A schedule contains two or more transactions executed together or one after another.


28) How can the schedule be classified?

Ans: A schedule can be classified in mainly two ways,

  1. On the basis of serializability
  2. On the basis of recoverability

29) What are blind writes?

Ans: When the update occurs without knowing or accessing previous value of data items are called blind updation or blind writes.


30) What are the various methods of concurrency control?

Ans: There are various concurrency control techniques like Time stamping protocol, Locked based protocol, Optimistic concurrency.


31) What is the trigger?

Ans: A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE, or UPDATE) occurs.


32) Which level of locking provides more concurrency in a relational database?

Ans: Row-level provides the highest degree of concurrency in a relational database.


33) What is VDL?

Ans: VDL is view definition language which specifies user’s views and their mapping to the conceptual schema.


34) What is a checkpoint?

Ans: A checkpoint is like a snapshot of the DBMS state. By taking checkpoint the DBMS can reduce the amount of work to be done during restart.


35) What is Deadlock?

Ans: Deadlock occurs when two transactions are each waiting on a resource that the other transaction holds.




36) What is the use of DBCC Command?

Ans: DBCC stands for database consistency checker. We use these commands to check the consistency of the database.


37) What is Thomas write rule?

Ans: In Thomas write rule we suggest a modification in time stamping protocol when the attempt writes request.


38) What is the recoverable schedule?

Ans: A schedule is said to be recoverable if in case of failure the dependent schedule has a chance of rollback.


39) What is cascading rollback?

Ans: It is the phenomenon in which a single transaction failure leads to a series of transaction rollbacks it is called cascading rollback.


40) What are instances?

Ans: The collection of information stored in the database at a particular moment is called instances.


41) In which fields the clustered index is built?

Ans: A clustered index is built on the Ordering non-key field.




42) Why the DBMS uses B and B+ trees for searching?

Ans: B and B+ tree keep the height of the tree smaller thus reduce searching time. These trees grow horizontally while other AVL, Red black trees grow vertically.


43) Why are B+ trees preferred over B tree?

Ans: The B+ tree is suitable for sequential and direct access. B+ tree height is less than that of B tree and all leaf nodes are at same level.


44) What is view?

Ans: A view may be a subset of a database or it may contain virtual data that is stored in the database files but is not explicitly stored.


45) What are important pieces of RDBMS architecture?

Ans: There are two important pieces of RDBMS first is kernel which is the software and other is data directory which consists of system level data structure.


46) How can we communicate with an RDBMS?

Ans: We can communicate with an RDBMS using SQL (structured query language).


47) What is a catalog?

Ans: A catalog is a table that consists the information such as the structure of each file, type, and storage format for each data item. The information stored in the catalog is called Metadata.


48) What is the order of clause?

Ans: ORDER by clause helps us to sort the data by ascending order or descending order.


49) What is Phantom read problem?

Ans: In phantom read problem, a transaction cannot repeat its read instruction because that variable is deleted by some other instruction.


50) What is join?

Ans: Joins helps in explaining the relationship between different tables. There are of two types – INNER JOIN and OUTER JOIN.

I hope you will like these DBMS Interview questions and answers, if you feel any difficulty in any question please write in the comment box.






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