SQL Basics

A database is a collection of data that is organized in a manner that facilitates ease of access, as well as efficient management and updating.

A database is made up of tables that store relevant information.

For example, you would use a database, if you were to create a website like PHPGurukul which contains lots of information like videos, usernames, passwords, and comments.

Database Tables

A table stores and display data in a structured format consisting of columns and rows that are similar to those in an Excel spreadsheet.

Databases often contain multiple tables, each designed for a specific purpose. For example, creating a database table of names and mobile numbers.

First, we would set up columns with titles firstName, lastName, and mobileNumber. Each table includes its own set of fields, based on the data it will store.

firstName	lastName	mobileNumber
Anuj	Kumar	1234567890
Atul	Singh	1122334455
Garima	Kapoor	123123000
John	Doe	2233112233
Rahul	Gupta	1425366633

A table has a specified number of columns but can have any number of rows.

Primary Key

A Primary Key is a field in the table that uniquely identifies the table record.

The primary key’s features:

• It must contain a unique value for each row.
• It cannot contain NULL values.

For example, our table contains a record of each name in the phone book. The unique id number would be a good choice for a primary key in the table, as there is always the chance for more than one person to have the same name

id	firstName	lastName	mobileNumber
1	Anuj	Kumar	1234567890
2	Atul	Singh	1122334455
3	Garima	Kapoor	123123000
4	John	Doe	2233112233
5	Rahul	Gupta	1425366633

What is SQL?

SQL stands for Structured Query Language.

SQL is used to access and manipulate a database.

SQL can:

• Insert, update, or delete records in a database.
• Create new databases, tables, stored procedures, and views
• retrieve data from a database, etc