DBMS interview questions

DBMS

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Qu-What is the difference between Cluster and Non cluster Index?

A clustered index reorders the way records in the table are physically stored. There can be only one clustered index per table. It makes data retrieval faster. A non clustered index does not alter the way it was stored but creates a complete separate object within the table. As a result insert and update command will be faster.

 

Qu-Explain the difference between DELETE, TRUNCATE and DROP commands?

Once delete operation is performed Commit and Rollback can be performed to retrieve data. But after truncate statement, Commit and Rollback statement can’t be performed. Where condition can be used along with delete statement but it can’t be used with truncate statement. Drop command is used to drop the table or keys like primary, foreign from a table.

Qu-What is a trigger?

Databases are set of commands that get executed when an event (Before Insert, After Insert, On Update, on delete of a row) occurs on a table, views.

 

Qu-What is the difference between Cluster and Non cluster Index?

A clustered index reorders the way records in the table are physically stored. There can be only one clustered index per table. It makes data retrieval faster. A non clustered index does not alter the way it was stored but creates a complete separate object within the table. As a result insert and update command will be faster.

 

Qu-What is Union, minus and Interact commands?

MINUS operator is used to return rows from the first query but not from the second query. INTERSECT operator is used to return rows returned by both the queries.

 

Qu-What is a stored procedure?

Stored Procedure is a function which contains collection of SQL Queries. Procedure can take inputs, process them and send back output.

 

Qu-What are the advantages a stored procedure?

Stored Procedures are precompiled and stored in database. This enables the database to execute the queries much faster. Since many queries can be included in a stored procedure, round trip time to execute multiple queries from source code to database and back is avoided.

 

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Data Base Management System

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Qu-What is a query?

A query with respect to DBMS relates to user commands that are used to interact with a

data base. The query language can be classified into data definition language and data manipulation language.

 

Qu-What is durability in DBMS?

Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.

 

Qu-What are partial, alternate,, artificial, compound and natural key?

  1. Partial Key: It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.
  2. Alternate Key: All Candidate Keys excluding the Primary Key are known as Alternate Keys.
  3. Artificial Key: If no obvious key either stands alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.
  4. Compound Key: If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.
  5. Natural Key: When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key

 

Qu-What is normalization?

It is a process of analyzing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties

(1).Minimizing redundancy, (2). Minimizing insertion, deletion and update anomalies

 

Qu-What is Functional Dependency?

A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y

 

Qu-What is Data Storage Definition Language?

The storage structures and access methods used by database system are specified by a set

of definition in a special type of DDL called data storage definition language.

 

Qu-What is DML (Data Manipulation Language)?

This language that enable user to access or manipulate data as organised by appropriate

data model.

  1. Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
  2. Non -Procedural DML or High level:DML requires a user to specify what data are

needed without specifying how to get those data.

Qu-What is DML Compiler?

It translates DML statements in a query language into low-level instruction that the query

evaluation engine can understand.

 

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Data Base Management System

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1. What is database?

A database is a collection of information that is organized. So that it can easily be accessed, managed, and updated.

 

2. What is DBMS?

DBMS stands for Database Management System. It is a collection of programs that enables user to create and maintain a database.

 

 3. What is a Database system?

The database and DBMS software together is called as Database system.

 

4.   What are the advantages of DBMS?

I.  Redundancy is controlled.

II. Providing multiple user interfaces.

III. Providing backup and recovery

IV. Unauthorized access is restricted.

V.  Enforcing integrity constraints.

 

5. What is normalization?

It is a process of analyzing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties –
(1).Minimizing redundancy, (2). Minimizing insertion, deletion and update anomalies.

 

6. What is Data Model?
A collection of conceptual tools for describing data, data relationships data semantics and constraints.

 

7. What is E-R model?

This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.

 

8. What is Object Oriented model?

This model is based on collection of objects. An object contains values stored in instance variables within the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.

 

9. What is an Entity?
An entity is a thing or object of importance about which data must be captured.

 

10. What is DDL (Data Definition Language)?

A data base schema is specifies by a set of definitions expressed by a special language called DDL.

 

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DBMS

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1. Software that defines a database, stores the data, supports a query language, produces reports and creates data entry screens is a:

A) Data dictionary

B) Database management system (DBMS)

C) Decision support system

D) Relational database

 

2. The separation of the data definition from the program is known as:

A) Data dictionary

B) Data independence

C) Data integrity

D) Referential integrity

 

3. In the client / server model, the database:

A) is downloaded to the client upon request

B) is shared by both the client and server

C) Resides on the client side

D) Resides on the server side

 

4. The database design that consists of multiple tables that are linked together through matching data stored in each table is called a:

A) Hierarchical database

B) Network database

C) Object oriented database

D) Relational database

 

5. Which of the following items is not the advantage of a DBMS?

A) Improved ability to enforce standards

B) Improved data consistency

C) Local control over the data

D) Minimal data redundancy

 

6. Which of the following statements is not correct?

A) All many-to-many relationships must be converted to a set of one-to-many relationships by adding a new entity

B) In a one-to-one relationship between two classes, the two classes are generally described by one table in relational database model

C) Encapsulation provides some security and control features

D) Properties and functions can be protected from other areas of the applications

 

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