To give you specific advice, we would need some more details of the
fields involved etc, so here's some general advice:
In your Master sheet, you could introduce a new column "Updated Price"
and use this to bring forward the price from the update sheet - if
there isn't one for a particular product code, then take the "Current
Price" from within the master sheet. Once you have the updates and have
applied the formula, then you could fix the values and use them to
overwrite "Current Price", thereby not having to change anything you do
to link to your website.
So, assuming you have been sent a file with an Update sheet in it. Open
it and your master file - adjust window sizes so that you can see both
on screen at the same time. Select the Update sheet and do a CTRL-drag
of the tab into your master file - this will copy the Update sheet into
your master file. You can close the window for the Update file, as you
don't need it anymore. (Incidentally, if the file only contains the
Update sheet, then it will be a bit quicker to just drag the tab into
the master file and then the Update file window will automatically
close).
In your "Updated Price" column on the master file, you would need a
formula along the lines of:
=IF(ISNA(VLOOKUP(A2,Update!A$2:B$500,2,0)),C2,VLOOKUP(A2,Update!A$2:B$500,2,0))
and copy this formula down your 4000 rows. Here I have assumed that
your Product_ID is in column A of both sheets and that each sheet has a
header row so that the data begins on row 2. I have also assumed that
your current price is in column C of the master sheet, and that your
update sheet has only 2 columns, with the price in column B - you will
have to amend these to suit your data.
Basically the formula says "if there is not an update price for this
Product ID then take the current price otherwise take the updated
price".
As mentioned earlier, you can fix these values in place (highlight all
the cells with the formula in, click <copy>, click Edit | Paste Special
| Values (check) | OK then <Esc>. This would then allow you to delete
the Update sheet, as it is no longer needed, and you can also copy the
values into column C to overwrite the Current Price (which is actually
yesterday's price at that point in time).
The next time you get an update of prices, you can repeat the
procedure.
Hope this helps.
Pete