Computer & IT Tips By Akash Padhiyar

Relational Databases

A relational database at its simplest is a set of tables used for storing data. Each table has a unique name and may relate to one or more other tables in the database through common values.


A table in a database is a collection of rows and columns. Tables are also known as entities or relations.


A row contains data pertaining to a single item or record in a table. Rows are also known as records or tuples.


A column contains data representing a specific characteristic of the records in the table. Columns are also known as fields or attributes.


A relationship is a link between two tables (i.e, relations). Relationships make it possible to find data in one table that pertains to a specific record in another table.


Each of a table’s columns has a defined datatype that specifies the type of data that can exist in that column. For example, the FirstName column might be defined as varchar(20), indicating that it can contain a string of up to 20 characters. Unfortunately, datatypes vary widely between databases.

Primary Keys

Most tables have a column or group of columns that can be used to identify records. For example, an Employeestable might have a column called EmployeeID that is unique for every row. This makes it easy to keep track of a record over time and to associate a record with records in other tables.

Foreign Keys

Foreign key columns are columns that link to primary key columns in other tables, thereby creating a relationship. For example, the Customers table might have a foreign key column called SalesRep that links to EmployeeID, the primary key in the Employees table.


The UPDATE is a SQL command used to edit/update existing records in a database table.

Relational Database Management System

A Relational Database Management System (RDBMS), commonly (but incorrectly) called a database, is software for creating, manipulating, and administering a database. For simplicity, we will often refer to RDBMSs as databases.


PostgreSQL is an object-oriented open source relational database management system, which uses a subset of SQL language.


Normalization is the process of organizing data to minimize redundancy and remove ambiguity. Normalization involves separating a database into tables and defining relationships between the tables. There are three main stages of normalization called normal forms. Each one of those stages increases the level of normalization. The 3 main normal forms are as follows:

  • First Normal Form (1NF): Each field in a table must contain different information.
  • Second Normal Form (2NF): All attributes that are not dependent upon the primary key in a database table must be eliminated.
  • Third Normal Form (3NF): No duplicate information is permitted. So, for example, if two tables both require a common field, this common field information should be separated into a different table.

There are 2 more normalization forms, fourth normal form (4NF) and fifth normal form (5NF), but they are rarely used. Normalization makes databases more efficient and easier to maintain.


A NULL value in a table is a value in a field that appears to be blank which means A field with a NULL value is a field with no value.

It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation

Data Integrity:

The following categories of the data integrity exist with each RDBMS:

  • 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.

Akash Padhiyar

I am Akash Padhiyar Founder of,BCA MCA Tutor ,Running Web development compnay "AkashInfoTech".

More Posts - Website - Facebook

Categories: SQL

3 Responses so far.

  1. Mortgage Rates says:

    Such a usefule blog…wow !!!!

  2. found your site on today and really liked it.. i bookmarked it and will be back to check it out some more later

  3. Wow, I never new that, much appreciated.

Leave a Reply

Google Search

Popular Posts

Web Designer vs Web Developer

Web Designer vs Web

This Infographic explain you what is role of Web Designer and ...

Download Bluestack Offline

Download BlueStack O

Download BlueStack Offline  BlueStack is software in which you can run ...

FireCMD user interface

Command Prompt (cmd.

Serious geeks spend a lot of time at the command ...