Inner join, sql confused

Question

This is the challeng for my class. Using INNER JOIN retrieve the following information:

1. Using the customers and orders table find all the orders that were created by an owner of a company.

I came up with this but when I enter it it says empty set>>>

SELECT id FROM orders INNER JOIN customers USING (id);

These are the columns from the customers table. CUSTOMERS

 | id   | company | last_name | first_name  | email_address | job_title       
 | business_phone  | home_phone | mobile_phone | fax_number | address 
 | city | state_province  |  zip_postal_code |  country_region  | web_page    
 | notes | attachments |.

These are the columns from the orders table. ORDERS

| id  | employee_id | customer_id | order_date | shipped_date | shipper_id           
| ship_name | ship_address | ship_city | ship_state_province  
| ship_zip_postal_code  | ship_country_region  | shipping_fee | taxes                
| payment_type | paid_date | notes | tax_rate | tax_status_id | status_id

Answer 1

When you write:

SELECT id FROM orders INNER JOIN customers USING (id);

you are requesting:

SELECT o.ID              -- or c.ID
  FROM Orders AS o
  JOIN Customers AS c
    ON O.ID = C.ID;

You're asking "which customers have an ID that is the same as an order ID?", which is probably not what you meant.

Most likely, you want to use some variant of:

SELECT o.ID AS Order_ID, c.ID AS Customer_ID
  FROM Orders AS o
  JOIN Customers AS c
    ON O.Customer_ID = C.ID;

You get to choose what information you get in the select list.

Answer 2

You can find examples of inner join syntax here. Here is one example of how to do this:

select o.* 
from orders o
inner join customers c on o.customer_id = c.id
/* not sure how "owner of company" is represented in the data, but I'm assuming it's some value for job_title */
where c.job_title = 'owner'