Introduction to RDBMS

RDBMS stands for Relational Database Management System.
RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
An RDBMS is a database management system (DBMS).
It is based on the relational model as introduced by E. F. Codd.
From 1970 to 1972, E.F. Codd published a paper to propose the use of a relational database model.
RDBMS is originally based on that E.F. Codd's relational model invention.
A relational database has the following major components:

The data in an RDBMS is stored in database objects which are called as tables.
This table is basically a collection of related data entries and it consists of numerous columns and rows.
Each table has a name in the database.

Every table is broken up into smaller entities called fields.
The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.
A field is a column in a table that is designed to maintain specific information about every record in the table.
A column is a vertical entity in a table that contains all information associated with a specific field in a table.

A record is a horizontal entity in a table.
Each row of a table is known as a record.
It is also known as tuple.
A record is also called a row of data is each individual entry that exists in a table.
For example, there are 7 records in the above CUSTOMERS table.

A domain is a set of permitted values for an attribute in the table.
For example, a domain of month-of-year can accept January, February,…December as values.
A domain of dates can accept all possible valid dates etc.
We specify the domain of attribute while creating a table.

Constraints are the rules enforced on data columns on a table.
These are used to limit the type of data that can go into a table.
This ensures the accuracy and reliability of the data in the database.
Constraints can either be column level or table level.
Column level constraints are applied only to one column whereas, table level constraints are applied to the entire table.
Example:

NOT NULL Constraint − Ensures that a column cannot have a NULL value.
DEFAULT Constraint − Provides a default value for a column when none is specified.
UNIQUE Constraint − Ensures that all the values in a column are different.
PRIMARY Key − Uniquely identifies each row/record in a database table.
FOREIGN Key − Uniquely identifies a row/record in any another database table.
CHECK Constraint − The CHECK constraint ensures that all values in a column satisfy certain conditions.
INDEX − Used to create and retrieve data from the database very quickly.

Data integrity is the maintenance of, and the assurance of the accuracy and consistency of data over its entire life-cycle, and is a critical aspect to the design, implementation, and usage of any system which stores, processes, or retrieves data.
Example:

Entity Integrity − There are no duplicate rows in a table.
Domain Integrity − Enforces valid entries for a given column by restricting the type, the format, or the range of values.
Referential integrity − Rows cannot be deleted, which are used by other records.
User-Defined Integrity − Enforces some specific business rules that do not fall into entity, domain or referential integrity.