SQL query language

SQL ( Structured Query Language ) is intended to process relational databases . Many SQL constructions and operators are associated with relational algebra interventions. From this point of view, relational algebra methods are essential for a deeper understanding of the use of the SQL language.

SQL language

The different DataBase Management Systems (DBMS) use two types of SQL language :

Interactive SQL : used to perform actions directly on the database in online mode. As a rule, some SQL server program accompanies interactive SQL. The most popular currently are Oracle SQL-Server, MS-SQL Server, Inter Base, and a few others.

Embedded SQL - Consists of SQL commands included directly in programs written in another programming language. For example, programming systems like Delphi, C ++ Builder, Visual Basic, Visual C ++ have SQL built in. In various DBMS, for example Microsoft -Access, there are also opportunities to use built-in SQL commands.

In the SQL language, there are many commands that relate to certain actions performed. Therefore, SQL can be divided into specific subsets:

•             DQL - query language, the commands are designed to extract data from tables.

•             DML - data manipulation language.

•             TPL - is a transaction processing language. The commands allow you to combine HTML language equipment into groups of transactions. If one of the commands cannot be executed, all previous commands in the same transaction are canceled - a "transaction rollback" occurs.

•             DDL - is a data definition language. It also includes data integrity instructions. For example, commands to create tables and organize relationships between them.

•             CCL - cursor control language. Allows you to select a row from the resulting query set for processing.

•             DCL - is a data management language. It contains instructions by which the assignment of access rights to the database, multiple tables or views is carried out.

SQL language functions

SQL (Structured Query Language): it is a structured query language. The language is oriented to work with relational (tabular) databases. The language is simple and in fact consists of (interpreted) commands, through which you can work with large data sets (databases), deleting, adding, changing information in them and conducting a convenient search.

To work with SQL code , you need a database management system (DBMS), which provides functionality for working with databases.

The Database Management System (DBMS) is a combination of language and software tools designed to create, maintain, and share a database by many users.

SQL components

The SQL language consists of the following components:

•             Data manipulation language (DML)

•             Data Definition Language (DDL)

•             Data Control Language (DCL)

1.            The Data Manipulation Language (DML) consists of 4 main commands:

•             Selecting information from the database - SELECT

•             Insert information into a database table - INSERT

•             Update (change) information in database tables - UPDATE

•             Delete information from a database - DELETE

2.            The Data Definition Language (DDL) is used to create and change the structure of the database and its components: tables, indexes, views (virtual tables), as well as triggers and storage procedures.

These are just some of the basic commands of the language:

•             Database creation - CREATE DATABASE

•             Table creation - CREATE TABLE

•             Table change (structure) - ALTER TABLE

•             Table Drop - DROP TABLE

3) The Data Control Language (DCL) is used to control data access rights and execute procedures in a multi-user environment.