/SQL

SQL Documentation

Introduction

SQL (Structured Query Language) is a standard programming language specifically designed for managing and manipulating databases. SQL allows you to create, read, update, and delete (CRUD) data stored in a relational database.

Creating and Managing a Database

1. Creating a Database

The CREATE DATABASE statement is used to create a new database.

CREATE DATABASE company_db;

2. Using a Database

To start working with a specific database, use the USE statement.

USE company_db;

3. Showing Tables

The SHOW TABLES statement is used to display all tables in the current database.

SHOW TABLES;

Creating and Managing Tables

1. Creating a Table

The CREATE TABLE statement is used to create a new table in the database.

CREATE TABLE employees (
    id INT PRIMARY KEY,
    first_name VARCHAR(50),
    last_name VARCHAR(50),
    department VARCHAR(50)
);

2. Viewing Table Structure

The DESCRIBE statement is used to display the structure of a table.

DESCRIBE employees;

3. Dropping a Table

The DROP TABLE statement is used to delete an existing table and its data.

DROP TABLE employees;

Basic SQL Queries

1. SELECT

The SELECT statement is used to retrieve data from a database.

SELECT column1, column2, ...
FROM table_name;

Example:

SELECT first_name, last_name
FROM employees;

2. WHERE

The WHERE clause is used to filter records that meet certain conditions.

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Example:

SELECT first_name, last_name
FROM employees
WHERE department = 'Sales';

3. INSERT INTO

The INSERT INTO statement is used to add new records to a table.

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

Example:

INSERT INTO employees (first_name, last_name, department)
VALUES ('John', 'Doe', 'Sales');

4. UPDATE

The UPDATE statement is used to modify existing records in a table.

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

Example:

UPDATE employees
SET department = 'Marketing'
WHERE last_name = 'Doe';

5. DELETE

The DELETE statement is used to delete records from a table.

DELETE FROM table_name
WHERE condition;

Example:

DELETE FROM employees
WHERE last_name = 'Doe';

Creating and Managing Views

1. Creating a View

The CREATE VIEW statement is used to create a view. A view is a virtual table based on the result set of an SQL statement.

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

Example:

CREATE VIEW sales_employees AS
SELECT first_name, last_name
FROM employees
WHERE department = 'Sales';

2. Querying a View

You can query a view just like a regular table.

SELECT column1, column2, ...
FROM view_name;

Example:

SELECT first_name, last_name
FROM sales_employees;

3. Dropping a View

The DROP VIEW statement is used to delete a view.

DROP VIEW view_name;

Example:

DROP VIEW sales_employees;

Conclusion

This documentation provides a basic overview of SQL and its fundamental operations. SQL is a powerful language for managing databases, and mastering its basics is essential for working with relational databases.