Question

I’m wondering if this would be the best way to build a table for an item that can have more than 1 price. Each product is identified by its model_number. Should I use a prefix before the model_number for each individual seller? I can’t use model_number for the primary key. For example:

seller_product_id      model_number     seller      price
SELLER_1_MODEL_NUMBER  MODEL_NUMBER     seller_1    9.99
SELLER_2_MODEL_NUMBER  MODEL_NUMBER     seller_2    19.99

Answer 1

For the sake of loose coupling, I suggest you build seperate Items and Price tables, and have another table (called Junction table) Item_Price which maps many items to many prices as you like.

This is called Many-to-Many relationship

Basically, it links an Item with its itemId to a Price with priceId, and stores this link in an Item_Price itemPriceId (or whatever you call the 3rd primary key)

Here’s a sample diagram EDIT: sorry about the previous diagram.

Here’s a sample SQL DDL of 3 tables, plus 2 junction tables to associate Item to Price, and Seller to Item.

CREATE TABLE Item (
    item_id int PRIMARY KEY,
    ..
    ..
)

CREATE TABLE Price (
    price_id int PRIMARY KEY,
    ..
    ..
)

CREATE TABLE Seller (
    seller_id int PRIMARY KEY,
    ..
    ..
)

-- This is the junction table for Item to Price mapping.
CREATE TABLE Item_Price (
    item_id int REFERENCES Item (item_id),
    price_id int REFERENCES Price (price_id),
    PRIMARY KEY (item_id, price_id)
)

-- This is the junction table for Seller to Item mapping.
CREATE TABLE Seller_Item (
    seller_id int REFERENCES Seller (seller_id),
    item_id int REFERENCES Item (item_id),
    PRIMARY KEY (seller_id, item_id)
)