Monday, 3 February 2020

Database Relational Model

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Database Relational Model


? The relation, which is a two-dimensional table, is the primary unit of storage in a relational
database.
? A relational database can contain one or more of these tables, with each table consisting of
a unique set of rows and columns.
? A single record is stored in a table as a row, also known as a tuple, while attributes of the
data are defined in columns, or fields, in the table.
? The characteristics of the data, or the column, relates one record to another.
? Each column has a unique name and the content within it must be of the same type.


Cross Product (*): This operator returns all the tuples of relation A plus all the tuples of
relation B.
Equi-Joins: Equi-join is same as conditional join, the only difference being only equity ‘=’
operator is used to join the two relations.
Joins: Joins are used to combine the information of two relations which have at least one field in
common.
Outer Joins: This is a special case “join” operator which considers the NULL values. Generally a
‘join’ operation performs the cross product of two tables and applies certain join conditions.

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