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Introduction

SQL (Structured Query Language) is a structured query language that allows you to perform operations on relational databases. SQL is a universal language used in most database management systems, including MySQL, PostreSQL, Microsoft Server SQL or Oracle Database.

SQL performs four different types of tasks, which are divided into the following groups:

  • DDL (Data Definition Language) - language for defining data; implements defining data structure
  • DML (Data Manipulation Language) - data manipulation language; performs data select and modification
  • DCL (Data Control Language) - data access control language
  • TCL (Transaction Control Language) - transaction control language; enables management of DML query groups.

SQL categories

SQL is not case sensitive, so you can use uppercase and lowercase letters interchangeably.

Comments

Like any other language, SQL also allows you to comment on the code. Use:

  • --, which ignores all characters to the end of the line
  • /* i */, which let you comment on many lines of code.