What is the lowest version of SQL Server you're writing this SP for and can you describe your exact problem in more details?

I assume you're trying to do some sort of FIFO inventory, right?

>>>I don't know a lot of concepts you used in your cte example. Hence, the reason to stay with what I know.
>>>
>>>Now, that I see the blueprint of how to use the Update and Select, I will try to modify your code to make it do other things I was looking for. Like, getting a Unit Price of the found record and reducing the value of @QtyUse (by what is "taken" from qty_left).
>>>
>>>Again, thank you.
>>>
>>>
>>Take a look at the OUTPUT clause of UPDATE command.
>
>I will. But I need to create this SP - completely - by Tuesday or Wednesday. I will probably mess up anyway, but if I work with new concepts, I will mess up for sure :)