Lesson 3	Examine Simple join
Objective	Examine how to use the WHERE statement to create a simple join.

SQL Joins Explained

The join is created when two key information items are related in a SELECT statement. You relate these items with the WHERE clause, creating a link between the different tables. Although you can create a join with several tables, for the purposes of this brief introduction, we will be using only two.
For reference, here are the tables:

Publishers Table

pub_id	pub_name	city	state	country
0736	New Moon Books	Boston	MA	USA
0877	Binnet & Hardley	Washington	DC	USA
1389	Algodata Infosystems	Berkeley	CA	USA
1622	Five Lakes Publishing	Chicago	IL	USA
1756	Ramona Publishers	Dallas	TX	USA
9901	GGG&G	München		Germany
9952	Scootney Books	New York	NY	USA
9999	Lucerne Publishing	Paris		France

Titles Table (a portion of the table is shown below)

title_id	pub_id	price	pubdate
BU1032	1389	19.99	Jun 12 1991 12:00AM
BU1111	1389	11.95	Jun 9 1991 12:00AM

The syntax of the WHERE clause is

...WHERE table1.column=table2.column

You are referencing the two different tables and the two columns that represent the information that links the two tables. For these tables, pub_id is common and will be used to create the join.
If you want the publisher's name for the book with the title ID of BU1032, the following statement will provide it:

SELECT pub_name FROM publishers, titles 
WHERE publishers.pub_id=titles.pub_id AND 
title_id='BU1032'

We are naming more than one table in the FROM clause. That makes sense because we're taking information from both the publishers and titles tables. Next, you can see where the relationship is called out:

publishers.pub_id=titles.pub_id.

That defines how these two tables are tied together. In this case, pub_id is the magic link between them.