Combining SQL queries into one with various having/group by/where rownum - sql

Question

I currently have three ORACLE SQL queries which are similar to this simplified example.
I get a list of customers which fulfill my requirements:
CREATE VIEW customerQRY AS
SELECT
o.customer_id,
o.order_id,
si.item_id,
o.price,
o.discount
FROM
Orders o
JOIN StockItems si ON o.order_id = si.order_id
WHERE
o.returned = 'N'
AND o.num_items = 1
AND o.completed = 'Y'
AND o.order_date BETWEEN TO_DATE('01-01-2019', 'DD-MM-YYYY') AND TO_DATE('01-01-2020', 'DD-MM-YYYY')
;
From those I get the top 1000 customers which have bought more than 10 items at max 10% discount:
CREATE TABLE CustomerSamples
SELECT
customer_id
FROM (
SELECT
customer_id
FROM
customerQRY
GROUP BY
customer_id
HAVING
COUNT(DISTINCT(order_id)) > 9
AND discount < 11
ORDER BY
COUNT(DISTINCT(order_id)) DESC,
discount DESC
)
WHERE
ROWNUM < 1001
;
Then I get all the data related to the order and items for this subset of customers:
(edit: this is actually not totally correct: I want the order details here to be a subset of the orders specified in CustomerSamples i.e. the ones which fall into the discount < 11 category; this can be done with a "where" clause here or however defined in a potential single query)
SELECT
Orders.*,
StockItems.*
FROM
CustomerSamples cs
JOIN Orders ON Orders.customer_id = cs.customer_id
JOIN StockItems ON StockItems.order_id = Orders.order_id
;
(please forgive any missed syntax errors as I've simplified the real ones - these run correctly in reality)
This is fair enough - it works - but I was asked to try and combine this into one query which makes sense for us with running on production boxes etc.
I have gone back and forth trying different things, but can't come up with a sensible solution!
Sure I can literally use customerQry as a subquery in the CustomerSamples, but this means I don't have the data from customerQRY and suddenly things get more complicated. I can't return order_ids from query 2 as we are grouping on the customer and counting the order_ids.
I can't see a way to get the 1000 customer_ids and their related order_ids in one go. I feel like I'm missing an obvious solution here, but I can't see it. Anyone have any ideas? Am I just fighting a waterfall?

Answer 1

If you use the texts of your request, then an example:
SELECT
Orders.*,
StockItems.*
FROM
Orders JOIN StockItems ON StockItems.order_id = Orders.order_id
WHERE
Orders.customer_id in (
SELECT
customer_id
FROM (
SELECT
customer_id
FROM
(
SELECT
o.customer_id,
o.order_id,
si.item_id,
o.price,
o.discount
FROM
Orders o
JOIN StockItems si ON o.order_id = si.order_id
WHERE
o.returned = 'N'
AND o.num_items = 1
AND o.completed = 'Y'
AND o.order_date BETWEEN TO_DATE('01-01-2019', 'DD-MM-YYYY') AND TO_DATE('01-01-2020', 'DD-MM-YYYY')
)
GROUP BY
customer_id
HAVING
COUNT(DISTINCT(order_id)) > 9
AND discount < 11
ORDER BY
COUNT(DISTINCT(order_id)) DESC,
discount DESC
)
WHERE
ROWNUM < 1001)
;