Additional rows needed in SQL view - mysql

Question

I have the following SQL tables, and require a solution compatible with both MySQL and Postgresql
create table price_level (
id serial primary key,
name varchar(200)
);
create table product (
id serial primary key,
name varchar(200),
base numeric not null,
vat int not null
);
create table product_price (
id serial primary key,
base numeric,
vat numeric,
product_id int not null references product(id) on update cascade on delete cascade,
price_level_id int not null references price_level(id) on update cascade on delete cascade,
unique(product_id,price_level_id)
);
For the SQL structure above I've created a view:
create view view_product as
select
p.id as product_id,
coalesce(pp.base, p.base) as base,
coalesce(pp.vat, p.vat) as vat,
pp.price_level_id
from
product as p
left join
product_price as pp on pp.product_id=p.id
;
These are sample data:
Table price_level
id name
1 A
2 B
3 C
4 D
5 E
Table product
id name base vat
1 Test 100 20
Table product_price
id base vat product_id price_level_id
1 NULL NULL 1 1
2 200 NULL 1 2
3 NULL 10 1 3
Output of the view view_product is:
product_id base vat price_level_id
1 100 20 1
1 200 20 2
1 100 10 3
... and the question is: How do I get output like this?:
product_id base vat price_level_id
1 100 20 1
1 200 20 2
1 100 10 3
1 100 20 4
1 100 20 5
As you see in the example above I need to get D and E price_level as additional rows. How do I create such view/join? It should have good performance also because tables can get big with additional price levels.
Thanks for help.

Answer 1

I would use union to add those records from price_level table that do not have corresponding record in product_price table for a certain product:
select
p.id as product_id,
coalesce(pp.base, p.base) as base,
coalesce(pp.vat, p.vat) as vat,
pp.price_level_id
from
product as p
left join
product_price as pp on pp.product_id=p.id
union distinct
select
p.id as product_id,
p.base,
p.vat,
pl.price_level_id
from
price_level pl
join
product as p
where (p.id, pl.id) not in (select product_id, price_level_id from product_price)

Answer 2

I would use following approach, cross join tables price_level and product. Then just lookup if override exists in product_price table.
SELECT
product.id as product_id,
IFNULL(product_price.base, product.base) as `base`,
IFNULL(product_price.vat, product.vat) as `vat`,
price_level.id as price_level_id
FROM price_level
CROSS JOIN product
LEFT JOIN product_price ON
product_price.price_level_id = price_level.id AND
product_price.product_id = product.id
WHERE product.id = 1
ORDER BY product.id, price_level.id
just remember to use product.id and not product_id in WHERE conditions

Answer 3

Try with:
create view view_product as
select
p.id as product_id,
coalesce(pp.base, p.base) as base,
coalesce(pp.vat, p.vat) as vat,
coalesce(pp.price_level_id,pl.id) --modified row
from
product as p
left join
product_price as pp on pp.product_id=p.id
LEFT JOIN price_level pl on pp.price_level_id=pl.id -- modified row
;
(not tested, but for sure you have to catch the price levels from the properly table)