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

ord_no      purch_amt   ord_date    customer_id  salesman_id
----------  ----------  ----------  -----------  -----------
70001       150.5       2012-10-05  3005         5002
70009       270.65      2012-09-10  3001         5005
70002       65.26       2012-10-05  3002         5001
70004       110.5       2012-08-17  3009         5003
70007       948.5       2012-09-10  3005         5002
70005       2400.6      2012-07-27  3007         5001
70008       5760        2012-09-10  3002         5001
70010       1983.43     2012-10-10  3004         5006
70003       2480.4      2012-10-10  3009         5003
70012       250.45      2012-06-27  3008         5002
70011       75.29       2012-08-17  3003         5007
70013       3045.6      2012-04-25  3002         5001

Sample table: customer

 customer_id |   cust_name    |    city    | grade | salesman_id 
-------------+----------------+------------+-------+-------------
        3002 | Nick Rimando   | New York   |   100 |        5001
        3007 | Brad Davis     | New York   |   200 |        5001
        3005 | Graham Zusi    | California |   200 |        5002
        3008 | Julian Green   | London     |   300 |        5002
        3004 | Fabian Johnson | Paris      |   300 |        5006
        3009 | Geoff Cameron  | Berlin     |   100 |        5003
        3003 | Jozy Altidor   | Moscow     |   200 |        5007
        3001 | Brad Guzan     | London     |       |        5005

Sample table: salesman

 salesman_id |    name    |   city   | commission 
-------------+------------+----------+------------
        5001 | James Hoog | New York |       0.15
        5002 | Nail Knite | Paris    |       0.13
        5005 | Pit Alex   | London   |       0.11
        5006 | Mc Lyon    | Paris    |       0.14
        5007 | Paul Adam  | Rome     |       0.13
        5003 | Lauson Hen | San Jose |       0.12

Sample Solution:

-- Selecting all columns from the result of natural joins between three tables: 'orders', 'customer', and 'salesman'
SELECT * 
-- Performing a natural join between 'orders' and 'customer' tables
FROM orders 
NATURAL JOIN customer  
-- Performing another natural join with the result of the previous join and the 'salesman' table
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.

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