SQL BASIC

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🧠 Part 1: Introduction to SQL (Structured Query Language)

💡 What is SQL?

SQL (Structured Query Language) is the standard programming language used to manage and manipulate relational databases. With SQL, you can:

• Create and modify database structures (schemas)

• Insert, update, delete, and retrieve data

• Control access to data (via permissions)

• Analyze data using aggregation and filtering

SQL works with relational database systems like:

• MySQL

• PostgreSQL

• SQLite

• SQL Server

• Oracle

SQL commands are grouped into five major categories:

Category	Description	Example
DDL (Data Definition Language)	Defines database structure	CREATE, ALTER, DROP
DML (Data Manipulation Language)	Deals with data modification	INSERT, UPDATE, DELETE
DQL (Data Query Language)	Fetches data	SELECT
TCL (Transaction Control Language)	Manages transactions	COMMIT, ROLLBACK
DCL (Data Control Language)	Manages access rights	GRANT, REVOKE

Part 2: Data Definition Language (DDL)

🔸 1. CREATE Statement

Used to create databases, tables, views, indexes, etc.

>> Syntax

CREATE TABLE table_name (

    column1 datatype,

    column2 datatype,

    ...

);

📌 Example:

CREATE TABLE Employees (
    EmpID INT PRIMARY KEY,
    Name VARCHAR(100),
    Age INT,
    Department VARCHAR(50)
);

🔸 2. ALTER Statement:

Modifies an existing table structure.

✅ Syntax:

SQL

ALTER TABLE table_name
ADD column_name datatype;

📌 Example:

SQL

ALTER TABLE Employees
ADD Salary DECIMAL(10,2);

🔸 3. DROP Statement

Deletes a table or database permanently.

📌 Example:

SQL 

DROP TABLE Employees;

⚠️ Note: This statement used to delete all the data of the table.

🧱 Part 3: Data Manipulation Language (DML)

🔸 1. INSERT INTO

Adds new data into a table.

✅ Syntax:

SQL

INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);

📌 Example:

INSERT INTO Employees (EmpID, Name, Age, Department)
VALUES (101, 'Amit Sharma', 28, 'HR');

🔸 2. UPDATE

Modifies existing records in the table

✅ Syntax:

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

📌 Example

UPDATE Employees
SET Salary = 55000
WHERE EmpID = 101;

NOTE: Always use WHERE to avoid updating all rows by mistake.

🔸 3. DELETE

Removes records from a table but the Structured of the table will remain same.

📌 Example:

DELETE FROM Employees
WHERE Age < 25; (This will only delete the data <25)
but If you want to delete entire data from the Table)

QUERY: DELETE FROM TABLE_NAME

🔍 Part 4: Data Query Language (DQL)

🔸 SELECT Statement

Used to retrieve data from a table.

✅ Syntax:

SELECT column1, column2
FROM table_name
WHERE condition;

📌 Example:

SQL 

SELECT Name, Department
FROM Employees
WHERE Salary > 50000;