Database relation many to many

Answer 1

I'm not sure I understand your exact scenario, but to create a many-to-many relationship, you simply create a "relationship table", in which you store id's for the two records you want to link.

Example:

Products
********
ProductID (PK)
Price

Retailers
*********
RetailerID (PK)
Name

ProductRetailerRelationships
****************************
ProductID
RetailerID

Answer 2

A many-to-many relationship is almost always modeled using an intermediate table. For your example,

Product
--------
prod_numero
...

Size
--------
size_numero
...

Product_Size
--------
prod_numero
size_numero
...

The Size table would contain particular sizes (say, 10 liter) and the Product_Size table creates a Product and Size pairing.

Answer 3

You Will need an Intermediary, or "Join" Table

ProductSizes
.......................
ProductID
SizeID

One record for each product-size combination