SQL Tutorial Introduction

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SQL Tutorial Introduction


What is SQL?


  • SQL is a language used to retrieve and manipulate data in a RDMS.
  • SQL stands for Structured Query Language.
What is a Database?


  • A database is a place to store data.
  • A relational database system (RDMS) stores data in tables.

Relational Database Tables


A relational database stores data in tables. Each table has a number of rows and columns.
The table below has 4 rows and 3 columns.

[Image: sql-table.jpg]



SQL and Relational Databases

A relational database contains tables which store data that is related in some way.
SQL is the language that allows retrieval and manipulation of table data in a relational database.

The database below has 2 tables: one with data on Users and another with data on Products.


[Image: sql-database.jpg]



Example database

This tutorial uses a database which is a modernized version of Microsoft's Northwind database. Northwind is a fictitious store that sells specialty food products from all over the world. The database has 5 tables.

Below is an Entity Relationship Diagram (ERD) which shows the tables and their relationships.
[Image: sql-model.jpg]
[Image: 5c8f08b5fe55e12baae6fc54e46c343a.gif]




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