SQL Exercises: Customer lives in a city other than the salesman's

SQL Query on Multiple Tables: Exercise-3 with Solution

From the following tables, write a SQL query to find those salespeople who generated orders for their customers but are not located in the same city. Return ord_no, cust_name, customer_id (orders table), salesman_id (orders table).

Sample table: salesman

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 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: 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 Solution:

-- This query selects specific columns ('ord_no', 'cust_name', 'orders.customer_id', 'orders.salesman_id') from the 'salesman', 'customer', and 'orders' tables.
-- It retrieves data where the 'city' column in the 'customer' table is not equal to the 'city' column in the 'salesman' table.
-- Additionally, it ensures that the 'customer_id' column in the 'orders' table matches the 'customer_id' column in the 'customer' table,
-- and the 'salesman_id' column in the 'orders' table matches the 'salesman_id' column in the 'salesman' table.
SELECT ord_no, cust_name, orders.customer_id, orders.salesman_id
-- Specifies the tables from which to retrieve the data (in this case, 'salesman', 'customer', and 'orders').
FROM salesman, customer, orders
-- Specifies the conditions for joining the tables and filtering the data.
WHERE customer.city <> salesman.city
  AND orders.customer_id = customer.customer_id
  AND orders.salesman_id = salesman.salesman_id;

Output of the query:

ord_no	cust_name	customer_id	salesman_id
70004	Geoff Cameron	3009		5003
70003	Geoff Cameron	3009		5003
70011	Jozy Altidor	3003		5007
70001	Graham Zusi	3005		5002
70007	Graham Zusi	3005		5002
70012	Julian Green	3008		5002

Code Explanation:

The said query in SQL that joins the 'salesman', 'customer', and 'orders' tables. The result set includes the order number (ord_no), customer name (cust_name), customer ID (customer_id), and salesman ID (salesman_id). The WHERE clause specifies multiple conditions for the join.
There is a first condition that must be fulfilled in order for the city column in the customer table to not be the same as the city column in the salesman table.
The second and third conditions specify the join conditions between the orders table and the customer and salesman tables, respectively, which is that the customer_id and salesman_id columns of the orders table must be equal to the corresponding columns in the customer and salesman tables.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

Visual presentation :

Practice Online

Query Visualization:

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Note: The pictorial represetation above is based on hypothetical table for the purpose of explanation only. Your answer may not match.

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