SQL Server Interview Questions and Answers

What is database?
ANSWER:
A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.

What is a Database system?
ANSWER:
The database and DBMS software together is called as Database system.

Disadvantage in File Processing System?
ANSWER:
• Data redundancy & inconsistency.
• Difficult in accessing data.
• Data isolation.
• Data integrity.
• Concurrent access is not possible.
• Security Problems. .

Define the "integrity rules"
ANSWER:
There are two Integrity rules.
• Entity Integrity: States that “Primary key cannot have NULL value”
• Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.

What is extension and intension?
ANSWER:
Extension -It is the number of tuples present in a table at any instance. This is time dependent.
Intension - It is a constant value that gives the name, structure of table and the constraints laid on it.

What is System R? What are its two major subsystems?
ANSWER:
System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center . It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.
Its two subsystems are
• Research Storage
• System Relational Data System.

How is the data structure of System R different from the relational structure?
ANSWER:
Unlike Relational systems in System R
• Domains are not supported
• Enforcement of candidate key uniqueness is optional
• Enforcement of entity integrity is optional
• Referential integrity is not enforced

What is a view? How it is related to data independence?
ANSWER:
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence. .

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

What is E-R model?
ANSWER:
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.

What is Object Oriented model?
ANSWER:
This model is based on collection of objects. An object contains values stored in instance variables with in 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.

What is an Entity?
ANSWER:
It is a 'thing' in the real world with an independent existence.

What is an Entity type?
ANSWER:
It is a collection (set) of entities that have same attributes.

What is an Entity set?
ANSWER:
It is a collection of all entities of particular entity type in the database.

What is an Extension of entity type?
ANSWER:
The collections of entities of a particular entity type are grouped together into an entity set.

What is Weak Entity set?
ANSWER:
An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.