Fetch data with default rows - mysql

Question

Suppose we have tables resource, item and price:
item
+--------+---------+
| itemId | name |
+--------+---------+
| 2743 | Product |
+--------+---------+
resource
+------------------+-----+----------------+--+
|resourceId | key | value | groupId |
+-----------+-----+----------------+---------+
| 45 | 1 | Client | 3 |
| 46 | 2 | Manufacturer | 3 |
| 69 | 1 | Delivery | 4 |
| 70 | 2 | Collection | 4 |
| 71 | 3 | Assembly | 4 |
| 72 | 4 | Client Request | 4 |
| 73 | 1 | Draft | 5 |
| 74 | 2 | Not Confirmed | 5 |
| 75 | 3 | Confirmed | 5 |
+-----------+-----+----------------+---------+
price
+---------+-----------+--------+----------+
| priceId | serviceId | itemId | price |
+---------+-----------+--------+----------+
| 294 | 4 | 0 | 20.0000 |
| 293 | 3 | 0 | 20.0000 |
| 292 | 2 | 0 | 20.0000 |
| 291 | 1 | 0 | 20.0000 |
| 290 | 1 | 2743 | 18.4000 |
| 288 | 1 | 2738 | 10.0000 |
| 267 | 4 | 2721 | 0.0000 |
| 266 | 3 | 2721 | 0.0000 |
| 265 | 2 | 2721 | 0.0000 |
+---------+-----------+--------+----------+
Rows in table resource with groupId=4 are services. They are refered to via column key from table price (serviceId). As you can see I have default prices for those services (first four rows in price with itemId=0). I need to fetch as many pirce rows as there are services for a given item. If that item doesn't have a price for a service, service's default price should be fetched. For example, the item with id = 2743 has price for service Delivery. For all other services their default prices should be returned. What I need is a result like this:
+---------+-----------+--------+----------+-----------+-----+----------------+---------+
| priceId | serviceId | itemId | price |resourceId | key | value | groupId |
+---------+-----------+--------+----------+-----------+-----+----------------+---------+
| 290 | 1 | 2743 | 18.4000 | 69 | 1 | Delivery | 4 |
| 292 | 2 | NULL | 17.0000 | 70 | 2 | Collection | 4 |
| 293 | 3 | NULL | 13.0000 | 71 | 3 | Assembly | 4 |
| 294 | 4 | NULL | 9.0000 | 72 | 4 | Client Request | 4 |
+---------+-----------+--------+----------+-----------+-----+----------------+---------+
Here is a query I tried. I get as many rows as services, but all of them have have the same price (that of the item)
SELECT *
FROM `price` AS `p`
INNER JOIN `item` ON p.id = item.id
RIGHT JOIN `resource` AS `res` ON 1 = 1
WHERE (res.groupId = 4)
AND (p.itemId = 2743);

Answer 1

select i.itemId, coalesce(p1.price, p0.price)
from item i
cross join price p0
left join price p1
on p1.serviceId = p0.serviceId
and p1.itemId = i.itemId
where i.itemId = 2743
and p0.itemId = 0