SQL Join
BCIS1013 / IS251 – Database System
Ms Nurfarahhanis Abdul Rasid
Copyright @2024 by UNIMY University of Computer Science & Engineering
Information Classification-Restricted
Introduction
• SQL joins are the foundation of database
management
systems,
enabling
the
combination of data from multiple tables
based on relationships between columns.
• Joins allow efficient data retrieval, which is
essential
for
generating
meaningful
observations and solving complex business
queries.
(INNER) JOIN
• (INNER) JOIN: Returns records that have matching
values in both tables.
• Syntax:
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name =
table2.column_name;
(INNER) JOIN
• Example : Show book titles along with their authors
Books
id
title
1
2
Time to Grow
Up!
Your Trip
3
4
5
Lovely Love
Dream Your Life
Oranges
6
Your Happy Life
7
Applied AI
8
My Last Book
Authors
type
author
_id
original 11
editor_ transla
id
tor_id
21
transla
ted
original
original
transla
ted
transla
ted
transla
ted
original
15
22
14
11
12
24
24
25
31
15
22
33
13
23
34
11
28
32
id
first_name
last_name
11
Ellen
Writer
12
Olga
Savelieva
13
Jack
Smart
14
Donald
Brain
15
Yao
Dou
(INNER) JOIN
• Example : Show book titles along with their authors
SELECT b.id, b.title, a.first_name, a.last_name
FROM books b
INNER JOIN authors a
id title
first_name last_name
ON b.author_id = a.id
1 Time to Grow Up! Ellen
Writer
ORDER BY b.id;
2
Your Trip
Yao
Dou
3
Lovely Love
Donald
Brain
4
Dream Your Life
Ellen
Writer
5
Oranges
Olga
Savelieva
6
Your Happy Life
Yao
Dou
7
Applied AI
Jack
Smart
8
My Last Book
Ellen
Writer
LEFT (OUTER) JOIN
• LEFT (OUTER) JOIN: Returns all records from the left
table, and the matched records from the right table.
• Syntax:
SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name =
table2.column_name;
LEFT (OUTER) JOIN
• Example: Display all books with their editors, if any.
Books
id
title
1
2
Time to Grow
Up!
Your Trip
3
4
5
Lovely Love
Dream Your Life
Oranges
6
Your Happy Life
7
Applied AI
8
My Last Book
type
author
_id
original 11
editor_ transla
id
tor_id
21
transla
ted
original
original
transla
ted
transla
ted
transla
ted
original
15
22
32
14
11
12
24
24
25
31
15
22
33
13
23
34
11
28
Editors
id
21
22
23
24
25
26
27
first_name
Daniel
Mark
Maria
Cathrine
Sebastian
Barbara
Matthew
last_name
Brown
Johnson
Evans
Roberts
Wright
Jones
Smith
LEFT (OUTER) JOIN
• Example: Display all books with their editors, if any.
SELECT b.id, b.title, e.last_name AS editor
FROM books b
LEFT JOIN editors e
id
title
ON b.editor_id = e.id
1
Time to Grow Up!
ORDER BY b.id;
editor
Brown
2
Your Trip
Johnson
3
Lovely Love
Roberts
4
Dream Your Life
Roberts
5
Oranges
Wright
6
Your Happy Life
Johnson
7
Applied AI
Evans
8
My Last Book
NULL
RIGHT (OUTER) JOIN
• RIGHT (OUTER) JOIN: Returns all records from the right
table, and the matched records from the left table.
• Syntax:
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name =
table2.column_name
WHERE condition;
RIGHT (OUTER) JOIN
• Example: : Display all editors with their books.
Books
id
title
1
2
Time to Grow
Up!
Your Trip
3
4
5
Lovely Love
Dream Your Life
Oranges
6
Your Happy Life
7
Applied AI
8
My Last Book
type
author
_id
original 11
editor_ transla
id
tor_id
21
transla
ted
original
original
transla
ted
transla
ted
transla
ted
original
15
22
32
14
11
12
24
24
25
31
15
22
33
13
23
34
11
28
Editors
id
21
22
23
24
25
26
27
first_name
Daniel
Mark
Maria
Cathrine
Sebastian
Barbara
Matthew
last_name
Brown
Johnson
Evans
Roberts
Wright
Jones
Smith
RIGHT (OUTER) JOIN
• Example: : Display all editors with their books.
SELECT b.id, b.title, e.last_name AS editor
FROM books b
id
title
RIGHT JOIN editors e
ON b.editor_id = e.id
1
Time to Grow Up!
ORDER BY b.id;
2
Your Trip
editor
Brown
Johnson
3
Lovely Love
Roberts
4
Dream Your Life
Roberts
5
Oranges
Wright
6
Your Happy Life
Johnson
7
Applied AI
Evans
NULL
NULL
Jones
NULL
NULL
Smith
FULL (OUTER) JOIN
• FULL (OUTER) JOIN: Returns all records when there
is a match in either left or right table.
• Syntax:
SELECT column_name(s)
FROM table1
FULL JOIN table2
ON
table1.column_name
table2.column_name
WHERE condition;
=
FULL (OUTER) JOIN
• Example : Display all books and all editors.
Books
id
title
1
2
Time to Grow
Up!
Your Trip
3
4
5
Lovely Love
Dream Your Life
Oranges
6
Your Happy Life
7
Applied AI
8
My Last Book
type
author
_id
original 11
editor_ transla
id
tor_id
21
transla
ted
original
original
transla
ted
transla
ted
transla
ted
original
15
22
32
14
11
12
24
24
25
31
15
22
33
13
23
34
11
28
Editors
id
21
22
23
24
25
26
27
first_name
Daniel
Mark
Maria
Cathrine
Sebastian
Barbara
Matthew
last_name
Brown
Johnson
Evans
Roberts
Wright
Jones
Smith
FULL (OUTER) JOIN
• Example : Display all books and all editors.
SELECT b.id, b.title, e.last_name AS editor
FROM books b
id
title
FULL JOIN editors e
ON b.editor_id = e.id
1
Time to Grow Up!
ORDER BY b.id;
2
Your Trip
editor
Brown
Johnson
3
Lovely Love
Roberts
4
Dream Your Life
Roberts
5
Oranges
Wright
6
Your Happy Life
Johnson
7
Applied AI
Evans
8
My Last Book
NULL
NULL
NULL
Jones
NULL
NULL
Smith