List Customer And Product Without Sale - sql

Question

Need to show the following columns (3) using UNION to return:
All customers who do not have an invoice
All products that were not sold
Category: Is this related to "customer" or "product"? Print "customer or "product"
ID: Customer.id (category="customer") or product.id (category="product")
Name: customer.customer_name (category="customer") or product.product_name (category="product")
Tables:
Customer
id
customer_name
city_id
customer_address
contact_person
email
phone
Product
id
sku
product_name
product_description
current_price
quantity_in_stock
Invoice
id
invoice_number
customer_id
user_account_id
total_price
time_issued
time_due
time_paid
time_canceled
time_refunded
Invoice_Item
id
invoice_id
product_id
quantity
price
line_total_price
So far have the following:
SELECT
category,
CASE
WHEN category = 'customer' THEN c.id
WHEN category = 'product' THEN p.id
END AS 'id',
CASE
WHEN category = 'customer' THEN c.customer_name
WHEN category = 'product' THEN p.product_name
END AS 'name'
FROM
(
SELECT
CASE
WHEN c.id = c.id THEN 'customer'
WHEN p.id = p.id THEN 'product'
END as 'category'
FROM
customer as c
LEFT Join -- Left join to show all customers even those with & without invoices
invoice as i
ON c.id = i.customer_id
AND i.id IS NULL -- Gives me all customers who do not have an invoice
JOIN invoice_item as ii
ON i.id = ii.invoice_id
Join product p
ON p.id = ii.product_id
) tb1
UNION ALL
SELECT
category,
CASE
WHEN category = 'customer' THEN c.id
WHEN category = 'product' THEN p.id
END AS 'id',
CASE
WHEN category = 'customer' THEN c.customer_name
WHEN category = 'product' THEN p.product_name
END AS 'name'
FROM
(
SELECT
CASE
WHEN c.id = c.id THEN 'customer'
WHEN p.id = p.id THEN 'product'
END as 'category'
FROM
product as p
LEFT JOIN -- Left join to show all products even those that sold and not sold
invoice_item as ii
ON p.id = ii.product_id
AND ii.invoice_id IS NULL -- Gives me products that didnt sell
JOIN invoice as i
ON ii.invoice_id = i.id
) tb2
Open to any suggestions as I'm stuck trying to figure out how to show the category as either "product" or "customer". Thanks in advance!

Answer 1

Considering your data model and requirements, you should try the below SQLs. You can easily perform UNION with both the SQLs.
First SQL returns this list --> All customers who do not have an invoice
select 'customer' as category, c.id as id, customer_name as name
from customer c
left join invoice i on c.id = i.customer_id
where i.id is null
Second SQL returns this list --> All products that were not sold
select 'product' as category, p.id as id, product_name as name
from product p
left join invoice_item ii on p.id = ii.product_id
where ii.id is null;

Answer 2

Well, it is older than 6 months but still, answer would be:
select 'customer' as category, c.id as id, customer_name as name
from customer c
left join invoice i on c.id = i.customer_id
where i.id is null
union
select 'product' as category, p.id as id, product_name as name
from product p
left join invoice_item ii on p.id = ii.product_id
where ii.id is null;

Answer 3

SELECT 'customer' as category,id,customer_name FROM customer
WHERE id NOT IN(SELECT customer_id FROM invoice)
UNION
SELECT 'product' as category,id,product_name FROM product
WHERE id NOT IN(SELECT product_id FROM invoice_item);

Answer 4

The actual question is all customers details even those without invoices and all products even those which are not sold.
SELECT c.customer_name,
p.product_name,
Coalesce((ii.quantity), 0) AS quantity
FROM customer c
LEFT JOIN invoice i
on c.id = i.customer_id
LEFT JOIN invoice_item ii
ON ii.invoice_id = i.id
LEFT JOIN product p
ON ii.product_id = p.id
ORDER BY c.customerid,
p.product_id,
ii.id
UNION
SELECT 'N/A',
p.product_name,
0
FROM products p
ORDER BY p.id