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 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.