Selling multiple products from the store in bundles and managing SKUs

I'm selling some bundles / sets in my shop and I'm not sure if in the SKU section of each bundle I should write the SKUs of all the items included in that bundle, or should it have its own unique SKU.

Basically, I have limited items that I sell them both separately and in bundles, so I need a solution that covers the right number of each specific item's number in the inventory; for example if 1 item from item x is sold separately, then in the inventory number of bundles that include item x also should decrease 1 (minus 1).

What I did is I wrote the SKUs of all the items included in a bundle in the SKU of that bundle separating them by a comma ',' however it seems it won't work this way. I appreciate if anyone knows the solution for that.

Thank you

ive been asking about this seemingly simple thing for years. 

This is only possible by using a third party add-on that synchronises the inventory. These addons are usually aren't cheap, for example Trunk Inventory.