For Product.csv files the ID is the id_product the product will get in the database. If you do not set the switch force ID's, the value of the ID column in the CSV file is ignored and a new ID i generated by your MySQL server. So If you create your Product.csv and combinations.csv at the same time, use Force ID's. I don't see an use case where you do not want to use Force ID's if you have combinations. You have to load the product.csv, get the id from the system and enter that one in the id_product column of your combinations.csv? If you load product without combinations, it might be useful.
Personally I always generate an ID with the following rules:
- Brand Identifier (2 digits)
- Year (1 digit last number of the year 2020 => 0, 2021 =>1)
- Collection identifier (1 digit, 0= Winter Collection, 1 = Summer Collection)
- A counter within a Brand increases with every product and every combination of that brand (6 digits, you can reset this yearly if necessary)
I also store the product ID in the reference fields (of both the product and the combination). It allows you to easily find in the back-end all products of a brand, of a certain year, of the summer or winter collection.
I use the supplier_reference to store the sku code of the point of sale system my customers use (the leading stock management system). This allows me to synchronize stock with and report sales to the pos-system. But you could also store the number that you use to order the product with your supplier.
I have written some tooling that allows my customers to supply me with *.xlsx files, which contains a product and combination data combined. A row for each combination in which the product information repeats (or is left empty after the first row of that product). I process those files to generate the Product and Combination .csv files, generating the ID's and putting the correct image postions in the combination file, etc. I offer that as a service to my customers, they pay per file I process.
In my humble opinion you can not create product and combination cvs files without some automated processing. To sensitive to errors.