Relational Database:
A relational
database is a collection of relations or two-dimensional tables. The database
management system (DBMS) of a relational database is called relational database
management system (RDBMS). The RDBMS is
software of relational database. The below table list some of the popular RDBMS
software.
|
Database Name
|
|
Oracle
|
|
MySQL
|
|
Microsoft SQL Server
|
|
MS Access
|
|
DB2
|
|
SQL Anywhere (Sybase)
|
|
PostgreSQL
|
|
Teradata
|
|
Informix
|
|
Apache Derby
|
|
Derby or Java DB
|
Terminology:
The relational database theory uses several
terminologies. These relational database terminologies are equivalent to the
SQL database terminologies. The table below lists some of the most
important relational database terms and their SQL database equivalents.
|
SQL
|
Relational Database
|
Description
|
|
Table
|
Relation
|
Object of database. It is data
structure
|
|
Row
|
Tuple
|
Horizontal data entries in a table
|
|
Column name and Column value
|
Attribute name and Attribute value
|
Labeled members in a table and
values under that label
|
|
Set of column names
|
Relation scheme or attributes set
|
A Schema
|
Objects of RDBMS:
The below
table show you the objects of RDBMS.
|
Objects
|
Description
|
|
Tables
|
The basic unit of storage. It
composed of rows and columns
|
|
View
|
The Logical representation of
subsets of data from one or more tables
|
|
Sequence
|
used to generate primary key values
|
|
Index
|
It improves the performs of some
queries
|
|
Synonym
|
Alternative name given to an object
|
Constraints Applied to Tables:
The
constraints are used to enforce rules at table level. They also prevent
deletion of tables if there is any dependency. The below table list the valid constraint types.
|
Constraints
|
Description
|
|
NOT NULL
|
It does not allow null values in
table
|
|
UNIQUE
|
It enforces uniqueness in the
column in which they are specified. It allows null value and create
non-cluster index
|
|
Primary Key
|
It is the a column or set of column
that uniquely identifies the rest of the data in any given row. It does not
allow null value and create cluster index.
|
|
Foreign Key
|
A foreign key is a column in a
table and this column is a primary key of another table.
|
|
Check
|
Using this constraint user can
restrict possible attribute values for a column admissible once.
|
How a database table looks like?
The below
shown is the representation of RDBMS table when you use Oracle Database 10g express
edition.
