Anti Join with group/conditions - mysql

Question

Note: I have simplified the question since both that and the answer have become I believe more complex than intended.
I want to an an anti-join that has a condition other than just not existing in the first table.
Table Product / Manufacturer
Widget / Acme
Paddle / Acme
Ball / Acme
Gas / Exxon
Pump / Exxon
Table: Customer / Product
Karen / Ball
Bob / Paddle
Karen / Gas
Bob / Pump
A "normal" anti-join would find out which products have not been ordered via
Select Products from `Product / Manufacturer` as T1
Left Join `Customer / Product` as T2
On T2.Zip is NULL
However what I am looking for is which customers didn't order which products, in essence:
Select Products from `Product / Manufacturer`
where Manufacturer = 'Acme' that do not exist in `Customer / Product`
where Customer = 'Karen'
and
Select Products from `Product / Manufacturer`
where Manufacturer = 'Exxon' that do not exist in `Customer / Product`
where Customer = 'Karen'
and
Select Products from `Product / Manufacturer`
where Manufacturer = 'Acme' that do not exist in `Customer / Product`
where Customer = 'Bob'
and
Select Products from `Product / Manufacturer`
where Manufacturer = 'Exxon' that do not exist in `Customer / Product`
where Customer = 'Bob'
'
But as one query since there are 100s of "Customers" and 100s of Manufacturers.

Answer 1

If you want to exclude all products for a manufacturer for which no product from that manufacturer appears in any order...
Then that means that you only want to include only products from certain manufacturers...
Which manufacturers have had a product appear in an order ?
SELECT r.manufacturer
FROM products r
JOIN orders s
ON s.product = r.product
GROUP BY r.manufacturer
You can wrap that query in parens and include it as an inline view ...
SELECT p.*
FROM ( SELECT r.manufacturer
FROM product r
JOIN orders s
ON s.product = r.product
GROUP BY r.manufacturer
) q
JOIN product p
ON p.manufacturer = q.manufacturer
LEFT
JOIN orders o
ON o.product = p.Product
WHERE o.product IS NULL
There are other query patterns that will return an equivalent result.
FOLLOWUP
NOTE: The "breakdown by gender/hour" part wasn't made clear in the original specification.
The query pattern is very much the same. Use an inline view query to return a distinct list of manufacturers for each gender/hour.
Then join that set to the product table, to get every product from those manufacturer. That will included products that were ordered, as well as products that weren't ordered.
Then apply the anti-join pattern, to exclude the products that were ordered by gender/hour.
SELECT q.gender
, q.hour
, p.manufacturer
, p.product
FROM ( SELECT s.gender
, s.hour
, r.manufacturer
FROM orders s
JOIN product r
ON r.product = s.product
GROUP
BY s.gender
, s.hour
, r.manufacturer
) q
JOIN product p
ON p.manufacturer = q.manufacturer
LEFT
JOIN orders o
ON o.gender = q.gender
AND o.hour = q.hour
AND o.product = p.product
WHERE o.product IS NULL
If that's not clear, consider that the following query returns an equivalent set. The inline line view query t returns the set of all products from a manufacturer, by gender/hour.
This query is somewhat less efficient (at least in MySQL) due to the additional inline view. And while longer, it may be more understandable, since the view query t makes explicit the set of all possible rows that could be returned... every product by manufacturer/gender/hour. (To see that set, the view query t can be pulled out and run separately to see what it returns.)
In the outermost query, t is referenced as if it were a table. If it t were replaced by a simple table reference, the query would just be a simple anti-join. All rows from t excluding rows that have a match.
SELECT t.gender
, t.hour
, t.manufacturer
, t.product
FROM (
SELECT q.gender
, q.hour
, q.manufacturer
, p.product
FROM ( SELECT s.gender
, s.hour
, r.manufacturer
FROM orders s
JOIN product r
ON r.product = s.product
GROUP
BY s.gender
, s.hour
, r.manufacturer
) q
JOIN product p
ON p.manufacturer = q.manufacturer
) t
LEFT
JOIN orders o
ON o.gender = t.gender
AND o.hour = t.hour
AND o.product = t.product
WHERE o.product IS NULL
I recommend you get the set of rows returned first. Before you futz with adding a GROUP BY and a GROUP_CONCAT aggregate to collapse the rows.
If you want to group multiple values of "hour" into just "am" or "pm", you can use an expression (in place of "hour") that returns "am" or "pm". (Think in terms of that expression being another column in the table; but instead of referencing a column in the table, you use an expression that derives the value from other columns in the table.
IF(x.hour<12,'am','pm')