This page has 0 threads | Add post

Blogs

Finding our blogs useful? Please consider helping us to share more!

Writing inner joins and outer joins in SQL Part one of a six-part series of blogs
An in-depth SQL tutorial on how to create inner joins, left outer joins, right outer joins, full outer joins, cross joins and self-joins! Inner Joins, Outer Joins and Shake-it-all-about Joins (this blog) Creating Joins using your Mouse - the Query Editor Writing Inner Joins in SQL Full, Left and Right Outer Joins in SQL Cross Joins using SQL Self-Joins in SQL (joining a table to itself) This online training on joins is part of a longer tutorial on the whole of SQL. Naturally, Wise Owl also run a range of SQL training courses for individualas and (above all) for businesses.

Writing inner joins and outer joins in SQL

Part one of a six-part series of blogs

An in-depth SQL tutorial on how to create inner joins, left outer joins, right outer joins, full outer joins, cross joins and self-joins!

Inner Joins, Outer Joins and Shake-it-all-about Joins (this blog)
Creating Joins using your Mouse - the Query Editor
Writing Inner Joins in SQL
Full, Left and Right Outer Joins in SQL
Cross Joins using SQL
Self-Joins in SQL (joining a table to itself)

This online training on joins is part of a longer tutorial on the whole of SQL. Naturally, Wise Owl also run a range of SQL training courses for individualas and (above all) for businesses.

Posted by Andy Brown on 30 November 2012

Inner Joins, Outer Joins and Shake-it-all-about Joins

This blog aims to show - in an easy-to-understand way - just about everything useful there is to know about joining tables in T-SQL (the dialect of SQL used by SQL Server).

You can represent a join between tables in a database diagram - but how can you do this in SQL?

Our Example Database

Throughout the whole of this blog, I'll use the simple database shown above. Here are the two tables in this database:


The table of 4 authors	The table of 9 books

You will notice that there are mismatches between the tables:


One author has no books	Two books have no authors

A Summary of the Joins Available

Given the example above, you can use the following types of join (explained in more detail throughout the rest of this blog):

Type of join	What it would show
Inner	The 7 books and 3 authors which match up to each other.
Left outer join	The 4 authors (together with any books they've written).
Right outer join	The 9 books (together with their authors, where found).
Cross join	The 36 possible combinations of author and book.

As we'll discover, the concepts of right and left outer join are interchangeable, but I've assumed here the tables are joined from left to right.

A Venn Diagram View of the Tables

For those who remember their Venn diagrams from schoolday maths (or math, if you're reading this in the States), here's a summary of the number of records in each table:

There are 4 authors, but one of them hasn't written any books.

Generating the Sample Database

If you want to follow through the examples in the rest of this blog, run the following script in SQL Server Management Studio to generate the Bookshop database shown above:

-- create a new database

CREATE DATABASE Bookshop

USE Bookshop

-- create table of books

CREATE TABLE [tblBook](

[BookId] [int] IDENTITY(1,1) PRIMARY KEY NOT NULL,

[BookName] [varchar](100) NOT NULL,

[AuthorId] [int] NULL,)

-- add some books into table

SET IDENTITY_INSERT [tblBook] ON

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (1, N'The Day of the Triffids', 2)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (2, N'Girl with Dragon Tattoo', 1)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (3, N'The Chrysalids', 2)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (4, N'The Kraken wakes', 2)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (5, N'The girl who Played with fire', 1)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (6, N'Emma', 4)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (7, N'Pride and Prejudice', 4)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (8, N'The Hobbit', 5)

INSERT [tblBook] ([BookId], [BookName], [AuthorId]) VALUES (9, N'The Life of Pi', 6)

SET IDENTITY_INSERT [tblBook] OFF

-- create table of authors

CREATE TABLE [tblAuthor](

[AuthorId] [int] IDENTITY(1,1) PRIMARY KEY NOT NULL,

[FirstName] [varchar](50) NOT NULL,

[LastName] [varchar](50) NOT NULL

)

-- add authors

SET IDENTITY_INSERT [tblAuthor] ON

INSERT [tblAuthor] ([AuthorId], [FirstName], [LastName]) VALUES (4, N'Jane', N'Austen')

INSERT [tblAuthor] ([AuthorId], [FirstName], [LastName]) VALUES (2, N'John', N'Wyndham')

INSERT [tblAuthor] ([AuthorId], [FirstName], [LastName]) VALUES (3, N'Oliver', N'Owl')

INSERT [tblAuthor] ([AuthorId], [FirstName], [LastName]) VALUES (1, N'Stieg', N'Larsson')

SET IDENTITY_INSERT [tblAuthor] OFF

Before we start looking at the nitty-gritty of inner and outer join syntax, let's look first at a way to avoid writing any SQL altogether.

Parts of this blog
Inner Joins, Outer Joins and Shake-it-all-about Joins (this blog) Creating Joins using your Mouse - the Query Editor Writing Inner Joins in SQL Full, Left and Right Outer Joins in SQL Cross Joins using SQL Self-Joins in SQL (joining a table to itself)

Some other pages relevant to the above blogs include:

This blog has 0 threads

Add a new post

Book any course as classroom, onsite or online training, or as one-to-one consultancy

Free resources

Paid services

Getting help

Where we are

Where you are

Online

Transparent reviews

Delivery of courses

Nicer to work with

Reliable and established

Our training courses

C#

Excel

MySQL

Power Apps

Power Automate

Power BI and DAX

Python

Report Builder

SQL

SQL Server

VBA Macros

Other training resources

Blogs

Exercises

YouTube tutorials

YouTube shorts

Test your skills

Consultancy

Courseware

Self-paced courses

Newsletters

Publications

Our training venues

London

Manchester

Across the UK

At your site

Online

Why we are different

Hundreds of published reviews

Small class sizes

Outstanding courseware

Online classroom

(Almost) no cancellations

Wise Owl trainers only

Genuine integrity

Invoices after training

30+ years of Wise Owl

Our top 100 clients

BLOGS BY TOPIC

BLOGS BY AUTHOR