SQL (Structured Query Language)

What is SQL?

SQL → Structured Query Language is a standard that is developed for managing the relational databases.

Why we need it?

Every web application you use now internally uses the databases for storing information. That is how you get the data once you stored. We use SQL to store, retrieve, update and delete data in database (Even more will see that later).

So in a simple context, database uses collection of tables(imaging a spreed sheet in Excel) to store a data, and we uses the SQL to manipulate the data in those tables like retrieving, adding, updating, or deleting.

How SQL looks like?

We say SQL code as Command or Statement. Here is an sample SQL statement,

SELECT * FROM employees;

Looks confusing right? Don’t worry we will explain it in few minutes. Before understanding the command we will see the types of commands to get some more idea into it.

SQL Command Type:

SQL command types are categorized into four types,

1. DDL: Data Definition Language → Deals with table schema
2. DML: Data Manipulation Language → Manipulating the table data
3. DCL: Data Control Language →
4. TCL: Transaction Control Language →

Data Definition Language: