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Introduction

SQL ( Structured Query Language ) is a structured query language that allows operations to be performed on relational_databases. SQL is a universal language, used in most database management systems, incl. MySQL,PostreSQL, Microsoft Server SQL orOracle Database.

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

  • DDL (Data Definition Language) - data definition language; implements data structure definition
  • DML (Data Manipulation Language) - data manipulation language; performs data retrieval and modification
  • DCL (Data Control Language) - Data access control language
  • TCL (Transaction Control Language) - transaction control language; allows you to manage DML query groups.

SQL categories

SQL language is not case sensitive, so upper and lower case letters can be used interchangeably.

Comments

Like any other language, SQL also allows you to comment on the code. This can be done by:

  • --, which ignores all characters until the end of a line
  • /* and */, which allow you to comment out multiple lines of code.