SQL Exercises: Sort out the customer who made at least an order

SQL Query on Multiple Tables: Exercise-5 with Solution

From the following tables, write a SQL query to find those customers where each customer has a grade and is served by a salesperson who belongs to a city. Return cust_name as "Customer", grade as "Grade".

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 Solution:

-- This query selects specific columns ('customer.cust_name' with alias "Customer", 'customer.grade' with alias "Grade", 'orders.ord_no' with alias "Order No.") 
-- from the 'orders', 'salesman', and 'customer' tables.
-- It retrieves data where the 'customer_id' column in the 'orders' table matches the 'customer_id' column in the 'customer' table,
-- the 'salesman_id' column in the 'orders' table matches the 'salesman_id' column in the 'salesman' table,
-- and ensures that 'salesman.city' and 'customer.grade' are not NULL.
SELECT customer.cust_name AS "Customer", customer.grade AS "Grade", orders.ord_no AS "Order No."
-- Specifies the tables from which to retrieve the data (in this case, 'orders', 'salesman', and 'customer').
FROM orders, salesman, customer
-- Specifies the conditions for joining the tables and filtering the data.
WHERE orders.customer_id = customer.customer_id
  AND orders.salesman_id = salesman.salesman_id
  AND salesman.city IS NOT NULL
  AND customer.grade IS NOT NULL;

Output of the query:

Customer      |Grade|Order No|
--------------|-----|--------|
Nick Rimando  |  100|   70002|
Geoff Cameron |  100|   70004|
Brad Davis    |  200|   70005|
Nick Rimando  |  100|   70008|
Fabian Johnson|  300|   70010|
Geoff Cameron |  100|   70003|
Jozy Altidor  |  200|   70011|
Nick Rimando  |  100|   70013|
Graham Zusi   |  200|   70001|
Graham Zusi   |  200|   70007|
Julian Green  |  300|   70012|

Code Explanation:

The said query in SQL that joins the 'orders', 'salesman', and 'customer' tables. The result set includes the customer name (cust_name) with an alias "Customer", customer grade (grade) with an alias "Grade", and order number (ord_no) with an alias "Order No."
The WHERE clause specifies multiple conditions for the join. A join condition is specified by the first and second conditions between the orders table, and the customer and salesman table, respectively, which states that the customer_id and salesman_id columns of the orders table must match the columns of the customer table and the salesman table, respectively.
The third and fourth conditions specify that the city and grade columns of the salesman and customer tables must not be null, respectively.

Explanation :

Visual presentation :

Practice Online

Query Visualization:

Duration:

Rows:

Cost:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous SQL Exercise: Find out customers who made the order.
Next SQL Exercise: Customers served by a salesman and commission.