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SQL Basic

Getting started with SQL

Overview 

Structured Query Language (SQL) is a programming language that has a special-purpose designed for managing data in a Relational Database Management System (RDBMS). Other SQL-like languages exist and they can be used in Relational Data Stream Management Systems (RDSMS), or in "not-only SQL" (NoSQL) databases. 


SQL has 3 major sub-varieties: 

1. Data Definition Language (DDL): creates and modifies the structure of database; 

2. Data Manipulation Language (DML): performs Read, Insert, Update and Delete operations on the database; 

3. Data Control Language (DCL): controls the access of the database. 

The core DML operations are Create, Read, Update and Delete (CRUD for short) that can be performed by the statements INSERT, SELECT, UPDATE and DELETE. 

There is also a (recently added) MERGE statement which can perform all 3 write operations (INSERT, UPDATE, DELETE). 

Many SQL databases are implemented as client/server systems; the term "SQL server" describes such a database system. At the same time, Microsoft makes a database that is named "SQL Server". While that database speaks a dialect of SQL, information about that database is in this tag but belongs into the SQL Server documentation.

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