SQL Introduction

What is a Database?

  • A database is a place to store data.
  • A relational database system (RDMS) stores data in tables.
  • Each table has rows and columns, much like a spreadsheet.
  • Each row has one or more columns to store data values.

What is SQL?

  • SQL is a language used to retrieve and manipulate data in a RDMS.
  • SQL stands for Structured Query Language.
  • SQL is pronounced as S.Q.L. (ess-cue-ell) or as Sequel. They are used interchangeably.

Relational Database Tables

As an example, the table below has 4 rows and 3 columns.

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.
SQL is the language with which you retrieve data, update data, and remove data.

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 with information on Products, Suppliers, Customers, and Orders.

Below is an Entity Relationship Diagram (ERD) which shows the tables and their relationships.

Additional details of the data model are available on the Sample Database page.
You can also 'play' with a live database directly from your browser using our SQL Sandbox.

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