Adding a row to a table with table combine or something like it

[ilyakoslov]

So I have two tables, one of them I have the amount of product sold and on the other I have the amount of product in my storage. The problem is, when I do the LOOKUPVALUE to find the amount sold in a specific date sometimes it doesn't work. 

Let's say I have one product in my storage on month 1, if I sell it on month 2 the amount of product sold won't appear in my storage data since I don't have a row with 0 storage. I wanted to combine those two, so that I would add a row for each time this happens and the row added would have 0 storage or null for the amount stored column but it would have the amount sold. I hope you guys can understand this, but if you can't just ask and i'll try and explain it better

[Greg_Deckler]

@ilyakoslov LOOKUPVALUE is unreliable. Use MAXX(FILTER(...),...) instead.