如何编写SQL查询以检查一个表上的多对多关系是否是另一个表上多对多关系的子集？

Question

I have some models as follows:

Product:
  id
  name
  price

Order:
  id
  user
  created

OrderProduct:
  order_id
  product_id

Promo:
  id
  discount

PromoProduct:
  promo_id
  product_id

A promotion applies to an order if all products in the promotion are present in the order. How do I write a SQL query to find out what promotions apply to an order?

Answer 1

SELECT  *
FROM    promo p
WHERE   id NOT IN
        (
        SELECT  pp.promo_id
        FROM    promoProduct pp
        WHERE   pp.product_id NOT IN
                (
                SELECT  product_id
                FROM    orderProduct op
                WHERE   op.order_id = $order
                )
        )

Note that this will also return all promotions with empty product lists ("there ain't no plane in this hangar that I can't fly"). If that's a problem, you will need to throw in an additional check for non-emptiness of the promotions.

Answer 2

This should fulfil your criterion that all the products in the promo need to be part of the order - because of the q1.ct = q2.ct . q1.ct gives you a count of products per promo per order; q2.ct gives you a total count of products per order.

Obviously you can further join this to the Order and Promo tables to get whatever additional information you want in your result set.

SELECT q1.order_id, q1.promo_id FROM
( SELECT op.order_id, pp.promo_id, COUNT( op.product_id ) AS ct
FROM OrderProduct op INNER JOIN PromoProduct pp ON product_id
GROUP BY op.order_id, pp.promo_id ) q1

INNER JOIN

( SELECT pp.promo_id, COUNT( pp.product_id ) AS ct
FROM PromoProduct pp
GROUP BY pp.promo_id ) q2

ON q1.promo_id = q2.promo_id AND q1.ct = q2.ct

Answer 3

Using subqueries you can divide and conquer.

Create a query to find how many products are in each promo:

SELECT promo_id, COUNT(product_id) AS no_products
FROM PromoProduct
GROUP BY promo_id

Then create another to find how many products for each order are in a promo:

SELECT OP.order_id, PP.promo_id, COUNT(OP.product_id) AS no_products
FROM OrderProduct OP
INNER JOIN PromoProduct PP ON OP.product_id = PP.product_id
GROUP BY OP.order_id, PP.promo_id

Then join them together:

SELECT OP.order_id, PP.promo_id
FROM OrderProduct OP
INNER JOIN PromoProduct PP ON OP.product_id = PP.product_id
INNER JOIN (SELECT promo_id, COUNT(product_id) AS no_products
FROM PromoProduct
GROUP BY promo_id) PC ON PP.promo_id = PC.promo_id AND COUNT(OP.product_id) = PC.no_products
GROUP BY OP.order_id, PP.promo_id

That may need a little tweaking but you get the point.

Answer 4

You could left join a given promo's products to a given order's products, and if any orderproducts row(s) came back null it would mean that the order did not qualify for that promo, given your definition of what it takes to qualify for a promo.

EDIT:

        select promoproducts.productid, orderproducts.productid
        from promoproducts
        left join orderproducts
        on promoproducts.productid = orderproducts.productid
        where promoid = 'x' and orderid = 'y'

EDIT2: ignore above (see Quassnoi's comment); the approach I'm suggesting needs to be done as a LEFT JOIN to an inline view:

        select pp.productid as promoproduct, orderproduct
        from promoproducts pp
        left join 

          (
         select productid as orderproduct
           from orderproducts
           where orderid=1

         ) as op
         on pp.productid=op.orderproduct
          where promoid =1

EDIT3: instead of comparing the order to a specific promo ( where promoid = x ), it could be compared against all current promos:

          ...  where promoid in (select promoid from promos where startdate ... expirydate ...) 
           -- find current promos

The real-world advantage to this left-join approach is that it shows you all of the promos the order qualifies for as well as all of the promos it does not qualify for and which product(s) would have to be added to the order to qualify for a promo .

Answer 5

SELECT *
FROM 'order' o
INNER JOIN orderproduct op ON op.order_id = o.order_id
INNER JOIN PromoProduct p ON p.product_id = op.product_id
WHERE o.order_id = ?

Try that.. Though I think you should rename the order table, as it is a keyword in MySQL.