SQL SELF JOIN

The SELF JOIN is used to join the table to itself, assuming it as two tables.

  • Syntax of SELF JOIN –

SELECT A.column_name,B.column_name,... FROM Table A ,Table B WHERE condition ;

 

Example – Consider the Product table to use Self join.

Demo Table –

Product Table

Category

Region

City

Country

Customer_ID

Customer_name

Office Supplies

Central

Chicago

United States

SM-20950

Suzanne McNair

Technology

East

New York City

United States

AH-10465

Amy Hunt

Office Supplies

East

New York City

United States

AH-10465

Amy Hunt

Office Supplies

East

Dover

United States

EP-13915

Emily Phan

Office Supplies

East

Dover

United States

EP-13915

Emily Phan

Technology

West

Aurora

United States

TP-21565

Tracy Poddar

Office Supplies

West

Aurora

United States

TP-21565

Tracy Poddar

Office Supplies

East

Long Beach

United States

AR-10825

Anthony Rawles

Office Supplies

West

Pasadena

United States

HA-14920

Helen Andreada

Furniture

West

Pasadena

United States

HA-14920

Helen Andreada

 

Now, suppose we want to see those customers that belong to the same cities.

SELECT A.[Customer Name] AS Customer_Name1,B.[Customer Name] AS Customer_name2, A.City
FROM
[dbo].[Products] AS A , [dbo].[Products] AS B
WHERE A.[Customer ID] != B.[Customer ID]
AND A.City = B.City ;

 

This output is the small section of the output by executing the above query –

Customer_Name1

Customer_Name2

City

Aaron Bergman

Adam Bellavance

Seattle

Aaron Bergman

Adam Hart

Arlington

Aaron Bergman

Alan Hwang

Seattle

Aaron Bergman

Alejandro Ballentine

Seattle

Aaron Bergman

Alejandro Savely

Seattle

Aaron Bergman

Amy Cox

Seattle

Aaron Bergman

Andrew Gjertsen

Seattle

Aaron Bergman

Angele Hood

Seattle

Aaron Bergman

Ann Chong

Seattle

Aaron Bergman

Ann Steele

Seattle

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