Oracle/mySQL database - database

Question

I'm kinda new in databases and I need to solve this one:
client(NAME, CITY, STREET, NUMBER, BALANCE, CLIENT_CODE);
order(ORDER_NUMBER, CLIENT_CODE, PROVIDER_NAME, FUEL, QTY, DATE);
provider(PROVIDER_NAME, PROVIDER_ADRESS, FUEL_CODE, PRICE, STOCK);
fuel(FUEL_CODE, FUEL_NAME);
I've already tried (and succeeded I guess) to create an ALTER TABLE for provider and fuel named provider_fuel in order to solve many-to-many relationship, but I don't have any idea how I could create a connection between order and provider.
I've changed the entities like this:
provider(PROVIDER_ID, PROVIDER_ADRESS);
fuel(FUEL_CODE, FUEL_NAME);
provider_fuel(ID_ENTRY, ID_PROVIDER, ID_FUEL, PRICE, STOCK).
Is that even ok? If so, how can I make connections between all those entities in my database?
I have to mention that my app should allow clients to place orders from providers who have their specific fuels, prices and so on.

Answer 1

I would suggest the following table layouts:
address(ID_ADDRESS, CITY, STREET, NUMBER);
client(ID_CLIENT, NAME, ID_ADDRESS);
client_order(ID_CLIENT_ORDER, ID_CLIENT, RECEIVED_DATE);
client_order_detail(ID_CLIENT_ORDER_DETAIL, ID_CLIENT_ORDER, ID_PROVIDER, ID_PRODUCT,
ORDER_QTY, STATUS, DELIVERED_DATE); -- Status in ('OPEN', 'DELIVERED')
provider(ID_PROVIDER, NAME, ID_ADDRESS);
product(ID_PRODUCT, PRODUCT_NAME);
provider_product(ID_PROVIDER, ID_PRODUCT, PRICE, STOCK_QTY);
You can, if you like, expand this. For example, a provider might have multiple locations from which product can be supplied, in which case you'd need to re-work the single PROVIDER table into something like
PROVIDER(ID_PROVIDER, NAME)
PROVIDER_PRODUCT(ID_PROVIDER, ID_PRODUCT, PRICE)
PROVIDER_ADDRESS(ID_PROVIDER_ADDRESS, ID_PROVIDER, ID_ADDRESS)
and then rework PROVIDER_PRODUCT as
PROVIDER_ADDRESS_PRODUCT(ID_PROVIDER_ADDRESS, ID_PRODUCT, STOCK_QTY)
I suppose it's also possible that the price a provider charges might depend on the location from which it's shipped so you might need to change the model to accommodate that. The point is that there are many different ways to do this, and it depends very much on the requirements you have.
EDIT
To obtain the total value of an order using the tables above you'd use a query such as:
SELECT co.ID_CLIENT_ORDER, SUM(cod.ORDER_QTY * pp.PRICE) AS ORDER_TOTAL_VALUE
FROM CLIENT_ORDER co
INNER JOIN CLIENT_ORDER_DETAIL cod
ON cod.ID_CLIENT_ORDER = co.ID_CLIENT_ORDER
INNER JOIN PROVIDER_PRODUCT pp
ON pp.ID_PROVIDER = cod.ID_PROVIDER AND
pp.ID_PRODUCT = cod.ID_PRODUCT
GROUP BY co.ID_CLIENT_ORDER
ORDER BY co.ID_CLIENT_ORDER

Answer 2

You can put id_provider in order table and get the provider details by the id .For ex
Select *,p.price,p.fuel_code from order as o join provider as p on o.id_provider=p.id

Answer 3

Welcome to the Oracle database world!
You can make connections between tables or views using JOIN structure.
In your example, you can connect your tables like this:
SELECT od.* FROM order od, provider pd WHERE od.provider_name=pd.provider_name
Or you can write it like this. It's up to your style. But I prefer the first one.
SELECT od.* FROM order od INNER JOIN provider pd ON od.provider_name=pd.provider_name
But it's always better using NUMBER type columns in joins. So I suggest, create provider_id (NUMBER type) on 2 tables and join them.
There are 5 main types (INNER, OUTER, FULL, LEFT, RIGHT) of joins in SQL. Each of them provides different things.

Answer 4

If I understand correctly your database represents a market place where a client can buy different kinds of fuels from providers. So far you have used natural keys:
A client has some login code that identifys them (client_code).
A provider is identified by their name. Do you want this? That would mean a provider address stays constant and cannot change. That may or may not be desired. If the company JACOB'S FUELSHOP INC changes to THE FUELSHOP INC, do you want to treat it as the same company or a different one?
You also generate order numbers. Do you want them unique in your database, or per client or per provider? The order table's key would accordingly be either just order_number or order_number + client_code or order_number + provider_name.
Now you don't want to have one provider only sell one type of fuel, but various types. You introduce a bridge table. But in the same step you introduce technical IDs. Do you want to use technical IDs instead of natural keys?
You have provider(PROVIDER_ID, PROVIDER_ADRESS) where the provider's name is either missing or included in the address. This allows you to change the name later. But remember that you may want to store the name then with every order, as you may want to reprint it later or just say whether you placed the order with the legal company JACOB'S FUELSHOP INC or THE FUELSHOP INC. Technical IDs are fine, but you must remember to still keep unique constraints on the natural keys and think about consequences as the one just mentioned.
As to the fuel price: You are storing the current fuel price, but you are not storing the price when ordered. Add the price to the orders table.
As to your question: Order and provider are already linked by provider_name in the original design. In the new design you've introduced the provider_id. If you want to use this instead, put provider_id in the orders table. As mentioned, you may or may not want the provider name in that table, too.