DAY - 4
RDBMS Concepts
A
Relational Database management System (RDBMS) is a database management
system based on relational model introduced by E.F Codd. In relational model,
data is represented in terms of tuples (rows).
RDBMS is used to
manage Relational database. Relational database is a collection of
organized set of tables from which data can be accessed easily. Relational
Database is most commonly used database. It consists of number of tables and
each table has its own primary key.
What is Table?
In
Relational database, a table is a collection of data elements organised
in terms of rows and columns. A table is also considered as convenient
representation of relations. But a table can have duplicate tuples while
a true relation cannot have duplicate tuples. Table is the simplest form
of data storage. Below is an example of Employee table.
|
ID
|
Name
|
Age
|
Salary
|
|
1
|
Adam
|
34
|
13000
|
|
2
|
Alex
|
28
|
15000
|
|
3
|
Stuart
|
20
|
18000
|
|
4
|
Ross
|
42
|
19020
|
What is a Record ?
A
single entry in a table is called a Record or Row. A Record
in a table represents set of related data. For example, the above Employee
table has 4 records. Following is an example of single record.
|
1
|
Adam
|
34
|
13000
|
What is Field ?
A
table consists of several records(row), each record can be broken into several
smaller entities known as Fields. The above Employee table
consist of four fields, ID, Name, Age and Salary.
What is a Column ?
In
Relational table, a column is a set of value of a particular type. The
term Attribute is also used to represent a column. For example, in
Employee table, Name is a column that represent names of employee.
|
Name
|
|
Adam
|
|
Alex
|
|
Stuart
|
|
Ross
|
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