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Concepts of RDBMS

Introduction to Table:

In this scenario, the data in an RDBMS is stored in database objects which are known as tables. The database contains one or more tables. The  table  consists of columns and rows and is basically a collection of related data.

A table is the most common and simplest form of data storage in a relational database(RD) . The following  is an example of a EmployeeInfo table −

2Mark4912000/-United State

Introduction to Field:

Commonly, the field are columns in the table. In the table, the field is designed to maintain specific information about every record. The field in EmployeeInfo table consists of Id, Name, Age, Salary, Address .

Introduction to Row:

Each individual entry that exists in a table is known as row. Example, there are 3 records in the above EmployeeInfo table. Below is a single row of data or record  or row in the EmployeeInfo table −

2Mark4912000/-United State

Introduction to Column:

Columns are known as a vertical entity in a table that contains all information associated with a specific field in a table .

Example, a column in the EmployeeInfo table is Address which represents location as shown below −


Introduction to SQL Constraints:

The rules enforced on columns of a table is known as Constraints. The Constraints are used to limit the type of data that can go into a table. Constraints ensures the accuracy and reliability of the data in the database.

The constraints can be applied either column level or table level. The Column level constraints are applied only to one column and the table level constraints are applied to the entire table.

The  commonly used constraints available in SQL  are−

  • NOT NULL Constraint − Restricts a column to have a NULL value.
  •  DEFAULT Constraint − Set/Ensures a default value for a column when none is specified.
  • UNIQUE Constraint − Restricts  the duplicate  values in a column .
  • PRIMARY Key − Primary key are used to Uniquely identifies each row/record in a database table.
  • FOREIGN Key − Foreign key are used to Uniquely identifies a row/record in any another database table.
  • CHECK Constraint − The CHECK constraint  checks the certain conditions in a column.
  • INDEX − The INDEX are used to create and retrieve data from the database very quickly.