This document provides an introduction to Structured Query Language (SQL). SQL is the standard language used to communicate with relational database management systems (RDBMS) like MySQL, Oracle, and Microsoft Access. It allows users to store, manage and query data. SQL commands include data definition language (DDL) to define databases, data manipulation language (DML) to query and manipulate data, and other commands for transaction control, data control and more. SQL is portable, efficient, easy to learn, and supports features like joins that make it well-suited for client-server environments. While powerful, SQL can also be costly and lack some control for programmers compared to other database options.