# Joining two tables on a google sheet

Every day I will download a "product inventory" list from an third party source, the list is in the format like this:

Product Code Product Name Quantity
1 Apple 100
2 Pear 200
3 Banana 150
4 Grape 400

However, not all product shows up everyday. In the next day the report may look like this:

Product Code Product Name Quantity
1 Apple 120
3 Banana 200
4 Grape 320
5 Kiwi 80

And I want to be able to join these two tables and build an "product movement" report like the following

Product Code Product Name Delta
1 Apple +20
2 Pear -200
3 Banana +50
4 Grape -80
5 Kiwi +80

Could someone please give me some pointers on how to achieve this?

Put the first table in `Sheet1` starting at cell `A1`, and the second table in `Sheet2` starting at cell `A1`.

Then use this formula in `Sheet3`:

``````=arrayformula(
query(
{
if(
isnumber(Sheet1!A1:C) * (column(Sheet1!A1:C) = column(C1)),
- Sheet1!A1:C,
Sheet1!A1:C
);
Sheet2!A1:C
},
"select Col1, Col2, sum(Col3)
where Col1 is not null
group by Col1, Col2",
1
)
)
``````

Format the third column like this:

Format > Number > More formats > Custom number format > `+#,##0;-#,##0;±0`.