SQL
Database LanguageSQL (Structured Query Language) is a standardized programming language designed for managing and manipulating relational databases. It allows users to create, read, update, and delete data, as well as define database structures and control access permissions.
Core SQL Operations (CRUD)
- CREATE: Insert new data into tables
- READ: Query and retrieve data from tables
- UPDATE: Modify existing data in tables
- DELETE: Remove data from tables
Basic SQL Commands
-- Create a table
CREATE TABLE employees (
id INT PRIMARY KEY,
name VARCHAR(100),
email VARCHAR(100),
salary DECIMAL(10,2)
);
-- Insert data
INSERT INTO employees (id, name, email, salary)
VALUES (1, 'John Doe', 'john@example.com', 75000);
-- Query data
SELECT name, salary
FROM employees
WHERE salary > 50000;
-- Update data
UPDATE employees
SET salary = 80000
WHERE id = 1;
-- Delete data
DELETE FROM employees
WHERE id = 1;
Advanced SQL Concepts
- Joins: Combine data from multiple tables
- Subqueries: Nested queries within other queries
- Indexes: Improve query performance
- Views: Virtual tables based on query results
- Stored Procedures: Reusable database functions
- Triggers: Automatic actions on data changes
Popular SQL Database Systems
- MySQL: Open-source, widely used for web applications
- PostgreSQL: Advanced open-source database with rich features
- Microsoft SQL Server: Enterprise database solution
- Oracle Database: High-performance enterprise database
- SQLite: Lightweight, embedded database