SQL Exercises: Customers along with the salesmen who works for them

Last update on March 08 2025 07:43:36 (UTC/GMT +8 hours)

Customer-Salesperson Association

From the following tables, write a SQL query to locate all the customers and the salesperson who works for them. Return customer name, and salesperson name.

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:

-- This query selects specific columns ('customer.cust_name' and 'salesman.name') from the 'customer' and 'salesman' tables.
-- It retrieves data where the 'salesman_id' column in the 'salesman' table matches the 'salesman_id' column in the 'customer' table.
SELECT customer.cust_name, salesman.name
-- Specifies the tables from which to retrieve the data (in this case, 'customer' and 'salesman').
FROM customer, salesman
-- Specifies the condition for joining the 'customer' and 'salesman' tables based on the equality of the 'salesman_id' columns.
WHERE salesman.salesman_id = customer.salesman_id;

Output of the query:

cust_name	name
Nick Rimando	James Hoog
Brad Davis	James Hoog
Graham Zusi	Nail Knite
Julian Green	Nail Knite
Fabian Johnson	Mc Lyon
Geoff Cameron	Lauson Hen
Jozy Altidor	Paul Adam
Brad Guzan	Pit Alex

Code Explanation:

The given query in SQL that joins the 'customer' and 'salesman' tables based on the "salesman_id" column. The result set includes the customer name (cust_name) and salesman name (name). The WHERE clause specifies the join condition between the two tables, which is that the "salesman_id" column must be equal in both tables.

Relational Algebra Expression:

Relational Algebra Tree:

Explanation:

Visual presentation:

Practice Online

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For more Practice: Solve these Related Problems:

• Write a SQL query to display all customers with their assigned salespeople, including customers with no salesperson (showing NULL) using an outer join.
• Write a SQL query to list customers and their salespeople where both names start with the same letter.
• Write a SQL query to retrieve customer names and salesperson names, sorted alphabetically by customer names, while eliminating duplicate pairs.
• Write a SQL query to show customer and salesperson pairs, but only include those pairs where the salesperson’s commission exceeds 0.12.
• Write a SQL query to display customer names alongside their salesperson names, replacing missing salesperson names with the string 'Not Assigned'.

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Previous SQL Exercise: Customer and salesmen who lives in the same city.
Next SQL Exercise: Customer lives in a city other than the salesman's.