Showing posts with label dbms. Show all posts
Showing posts with label dbms. Show all posts
Cursor
1. Explain about cursors ?
A cursor is defined as a work area where SQL statement is executed.There are two types of cursors.
1.Implicit cursor
2.Explicit cursor
2. Give the attributes of the implicit cursors
The attributes of implicit cursors are:
%FOUND : true if the SQL DML statement returns a row or multiple rows to the cursor
%NOTFOUND :true if the SQL DML statement does not return a row to the cursor
%ISOPEN : to check whether cursor is open or not
%ROWCOUNT : display the number of results for a given SQL DML statement
3. Give an example how implicit cursor attributes can be used
CREATE OR REPLACE PROCEDURE DISPLAY_FLIGHT
AS
CURSOR DIS_FLI IS
SELECT * FROM FLIGHT WHERE SOURCE_CODE IN(SELECT CITY_CODE FROM CITY_MASTER WHERE CITY_NAME='MUMBAI');
REC_FLI DIS_FLI%ROWTYPE;
BEGIN
OPEN DIS_FLI;
LOOP
FETCH DIS_FLI INTO REC_FLI;
EXIT WHEN DIS_FLI %NOTFOUND;
DBMS_OUTPUT.PUT_LINE (REC_FLI.FID||' '||REC_FLI.FNAME||' '||REC_FLI.SOURCE_CODE||' '||REC_FLI.DESTINATION_CODE||' '||REC_FLI.JOURNEY_HOURS);
END LOOP;
END;
A cursor is defined as a work area where SQL statement is executed.There are two types of cursors.
1.Implicit cursor
2.Explicit cursor
2. Give the attributes of the implicit cursors
The attributes of implicit cursors are:
%FOUND : true if the SQL DML statement returns a row or multiple rows to the cursor
%NOTFOUND :true if the SQL DML statement does not return a row to the cursor
%ISOPEN : to check whether cursor is open or not
%ROWCOUNT : display the number of results for a given SQL DML statement
3. Give an example how implicit cursor attributes can be used
CREATE OR REPLACE PROCEDURE DISPLAY_FLIGHT
AS
CURSOR DIS_FLI IS
SELECT * FROM FLIGHT WHERE SOURCE_CODE IN(SELECT CITY_CODE FROM CITY_MASTER WHERE CITY_NAME='MUMBAI');
REC_FLI DIS_FLI%ROWTYPE;
BEGIN
OPEN DIS_FLI;
LOOP
FETCH DIS_FLI INTO REC_FLI;
EXIT WHEN DIS_FLI %NOTFOUND;
DBMS_OUTPUT.PUT_LINE (REC_FLI.FID||' '||REC_FLI.FNAME||' '||REC_FLI.SOURCE_CODE||' '||REC_FLI.DESTINATION_CODE||' '||REC_FLI.JOURNEY_HOURS);
END LOOP;
END;
Database Management System
What is data model?
Data
Model describes how data is connected to each other and how the data is
processed and how the data is stored in the system.
What is three schema architecture?
Three
schema architecture:
1.
Internal Level
2.
Conceptual Level
3.
External Level
1.
Internal Level: It is the lowest level of data abstraction that deals with the
physical representation of the database on the computer and it is also known as
physical level.
2.
Conceptual Level: This level describes how relationship is established amount
various data entities, how data is stored in the database.
3.
External Level: It deals with end user.
It permits users to access data in a way that is customized according to
their needs, so that the same data can be seen by different users in
different ways, at the same time.
Why would you choose a database system instead
of simply storing the data in Operating system files?
In
a Database system large amounts of data can be stored compared to operating
system files. Any kind of data can be stored in database system, where as
operating system files cannot store.
In
database, we can search and retrieve the data easily compared to operating
system files.
Data
is more secure and has less redundancy in database system when compared to operating
system files.
What are the different types of languages
supported in database?
There
are two different types of languages supported in database. They are
1.DDL
: Data Definition Language/ Data Description Language
2.DML
: Data Manipulation Language
DDL
defines the database schema. It is used to build and modify the structures of
databases.
DML
is used by the end users to store, retrieve or manipulate the data in the
databases.
What are the key stages in object oriented
relational database design?
The 6 stages in
object oriented relational database design are:
1.
Finding
the objects
2.
Make the
links
3.
Make all
links one to many
4.
Add the
primary keys
5.
Add the
foreign keys
6.
Add the
fields
What is linking in database?
Linking in database :
Establishing connection between different entities in the database.
What is primary Key?
Primary Key: The piece of information the database uses to
find a record
What is foreign Key?
Foreign Key: The piece of information the database uses to
link records in different tables
Who are the different types of users accessing
the database and in what way?
The
different types of users accessing the database are:
1.
Application Programmers
2.
Sophisticated users
3.
Specialised users
4.
End Users
1.
Application Programmers: the person who builds the database is called an
application programmer
2.
Sophisticated users : Sophisticated users interact with the system and form their query language
3.
Specialised users: The Specialised users write applications database
applications that do not fit into the traditional data processing framework.
4.
End Users : invoke one of the permanent application
programs that have been written previously. They use
the application to get their task done
What is a database? What is DBMS?
A
database is a collection of relational data.
DBMS
is a set of computer programs that controls the creation, maintenance and the
use of a database.
What is an entity?
An entity is any real thing that can be distinguished.
Explain weak entity?
A weak entity cannot be independent. It depends on other entities
What is an entity?
An entity is any real thing that can be distinguished.
Explain weak entity?
A weak entity cannot be independent. It depends on other entities
Define the following terms:
relation schema, relational database schema,
domain, attribute, attribute domain, relation instance, relation cardinality, and relation
degree.
domain, attribute, attribute domain, relation instance, relation cardinality, and relation
degree.
Relation
schema : A relation schema is a list of attribute names.
Relational
Database schema : A relational database schema is the tables, columns and
relationships that make up a relational database.
A relational database schema helps you to organize and understand the structure of a database.
A relational database schema helps you to organize and understand the structure of a database.
Domain
: Domain refers to all the values which a data element may contain.
Attributes
: Attributes are the set of values that define an entity
Attribute
domain ; It is the set of data values allowed in an attribute.
Relation
instance: A finite set of tuples in the relational database system represents
relation instance. Relation instances do not have duplicate tuples.
Relation
Cardinality: It specifies the number of each entity that is involved in the
relationship
Relation
Degree : Number of entities participating in the relationship
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