SQL

SQL (Structured Query Language) is the standard language for storing, reading, modifying and deleting data in relational databases. Applications and administrators use it to communicate with a database management system by issuing commands in a readable, declarative syntax close to plain English.

How SQL works

In a relational database, data is stored in tables made of rows and columns, linked to one another by relationships. SQL lets you operate on those tables, and its commands fall into several groups:

• DQL/DML — working with data: SELECT (read), INSERT (add), UPDATE (change), DELETE (remove),
• DDL — defining structure: CREATE, ALTER, DROP for tables and schemas,
• DCL/TCL — permissions and transactions: GRANT, REVOKE, COMMIT, ROLLBACK.

A SELECT query can filter data (WHERE), sort it (ORDER BY), group it (GROUP BY) and combine several tables (JOIN). Although the SQL standard is shared, individual systems — such as MySQL, PostgreSQL or MariaDB — add their own extensions.

SQL in practice

SQL is the foundation of nearly every data-driven web application: online stores, CMS platforms, SaaS apps and portals. Backend code sends SQL queries to fetch product data, save an order or authenticate a user. Knowing SQL is essential not only for developers but also for analysts and database administrators — and building queries safely protects an application from SQL injection attacks. On typical hosting and VPS servers, relational databases that speak SQL are available by default.