SQL

Introduction to SQL

SQL (Structured Query Language) is a standard programming language used to manage and manipulate relational databases. It is used to create databases, insert data, retrieve data, update records, and delete data.

SQL works with relational databases that store data in tables (rows and columns). It is easy to learn and widely used in industries such as banking, education, healthcare, and e-commerce.

 Types of SQL Commands

  • DDL (Data Definition Language) – CREATE, ALTER, DROP

  • DML (Data Manipulation Language) – INSERT, UPDATE, DELETE

  • DQL (Data Query Language) – SELECT

  • DCL (Data Control Language) – GRANT, REVOKE

  • TCL (Transaction Control Language) – COMMIT, ROLLBACK, SAVEPOINT

SQL is essential for interacting with relational database systems efficiently.

 Advanced SQL Features

Advanced SQL features provide powerful capabilities for handling complex queries and database operations.

 1️⃣ Joins

Used to combine data from multiple tables (INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN).

 2️⃣ Subqueries

Queries written inside another query to perform complex filtering.

 3️⃣ Aggregate Functions

Functions like COUNT(), SUM(), AVG(), MAX(), MIN() used for calculations.

 4️⃣ Grouping and Filtering

  • GROUP BY – Groups rows with similar values

  • HAVING – Filters grouped data

 5️⃣ Views

Virtual tables created using SELECT queries.

 6️⃣ Indexes

Improve the speed of data retrieval.

 7️⃣ Stored Procedures and Functions

Reusable SQL code stored in the database.

 8️⃣ Triggers

Automatically executed when certain database events occur.

Advanced SQL features help improve performance, maintainability, and efficiency in database systems.


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