Relational Database Model

What is RDBMS ?
It is an organized set of tables to store information so that we can access the information efficiently.
It is called as Relational because the values of each table are related with the value of every other table.

Examples of RDBMS are:
1) MySQL
2) Oracle
3) DB2
4) MS-Access
5) SQL Server

What is Table in RDBMS ?
-> It is a set of records that contains rows and columns.
-> It is a collection of data elements represented in a structured format in terms of rows and columns.
-> Each table is assigned a specific name.

Records and Fields

Record is a tuple/row and it is composed of attributes and contains data.

Field is also known as column/attribute. Each row is broken down into smaller entities(element) known as Fields.

Degree
It is the number of Fields(Attributes) in a relation.

Cardinality
It is the number of Rows(tuples) in a relation.

Cardinality in RDBMS is different from Cardinality in ER-Diagram.

Domain of a Field(Attribute)
It is all the possible values that a field can take.
Example: Month -> Jan to Dec

Null Value - It specifies that no value is associated with the attribute. It is represented by a blank space.

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