SQL Exercise: Join within the tables salesman, customer and orders

SQL JOINS: Exercise-7 with Solution

Write a SQL statement to join the tables salesman, customer and orders so that the same column of each table appears once and only the relational rows are returned.

Sample table: orders

Sample table: customer

Sample table : salesman

Sample Solution:

SELECT * 
FROM orders 
NATURAL JOIN customer  
NATURAL JOIN salesman;

Output of the Query:

salesman_id	city		customer_id	ord_no	purch_amt	ord_date	cust_name	grade	name		commission
5005		London		3001		70009	270.65		2012-09-10	Brad Guzan		Pit Alex	0.11
5001		New York	3002		70002	65.26		2012-10-05	Nick Rimando	100	James Hoog	0.15
5001		New York	3007		70005	2400.60		2012-07-27	Brad Davis	200	James Hoog	0.15
5001		New York	3002		70008	5760.00		2012-09-10	Nick Rimando	100	James Hoog	0.15
5006		Paris		3004		70010	1983.43		2012-10-10	Fabian Johnson	300	Mc Lyon		0.14
5001		New York	3002		70013	3045.60		2012-04-25	Nick Rimando	100	James Hoog	0.15

Explanation:

The said SQL query that uses the NATURAL JOIN clause to combine rows from three tables: orders, customer, and salesman.
The NATURAL JOIN clause compares all columns of the two joined tables and only returns the rows where the values match.
The query retrieves all columns from the three tables where the customer_id from the orders table matches the customer_id from the customer table, and the salesman_id from the orders table matches the salesman_id from the salesman table.
Note that using NATURAL JOIN can be dangerous if the tables have columns with the same name but different meanings, because it could lead to unexpected results.

Relational Algebra Expression:

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Previous SQL Exercise: Display commission of the salesman for an order.
Next SQL Exercise: Customer who works either through a salesman or by own.