Structured Query Language (SQL) is a programming language designed for managing relational database systems. SQL is a language used to create, modify, query, and manage data stored in a relational database management system (RDBMS). The purpose of SQL is to allow users to access and manipulate data in a database, regardless of the size or complexity of the data.

SQL was first proposed in the 1970s by Donald Chamberlin and Raymond Boyce of IBM, and was originally called SEQUEL (Structured English Query Language). The name was later changed to SQL by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO) in the 1980s.

SQL is widely used in modern database management systems like Oracle, MySQL, Postgres, SQLite, SQL Server, and IBM’s DB2. Each of these database management systems implements variations of the SQL language, although the core syntax remains the same.

SQL is the standard language for managing and manipulating relational database systems. Relational databases store data in a collection of tables, which can be linked together through relationships. SQL allows users to create, modify, and update tables, as well as perform complex queries that pull data from multiple tables.

SQL has separate commands for performing different operations. There are commands for creating tables and modifying them, for creating new records and updating existing ones, and for querying data from the tables.

There are several types of SQL commands, including Data Manipulation Language (DML) commands, Data Definition Language (DDL) commands, and Data Control Language (DCL) commands.

DML commands like SELECT, INSERT, UPDATE, and DELETE are used to access and manipulate data in a database. DDL commands like CREATE, ALTER, and DROP are used to create, modify and manage database schema and metadata. DCL commands like GRANT and REVOKE are used to manage database security and permissions.

SQL is easy to use and widely adopted, making it an essential skill for anyone working with data in any capacity. Learning SQL can help individuals to extract more meaningful insights from the data stored in their databases, and help businesses to make better-informed decisions.