Table autofill with serial number

[crtnAF]

Hello. I have been slightly frustrated by searching solution for my little specific issue.

I have a excel table where I register my invoices. As for usual autofill, when we start putting in any value right below the table - the table expands itself and inserts the formulas from the above rows.
What I need is an automatic unique row serial number/ID. My table is from several columns and the data might be filtered. Using the casual =ROW(A1) doesn't do the job, because the given number/id will not stick with the row when you sort the table differently.
For now I just put in a value by hand, but the problem is that the last entry could be filtered away, so I have to remember always to clear my filters and sort them in ascending order at serial number/ID column before I enter new row.

So the question is,
For the given example of table:

By not being afraid that the order is sorted differently and some rows might be hidden away (in example ID 4), I just start a new entry by entering next date below and it will autofill the table column [number/ID] with next unique number (should be 6 in this one)? And if I sort them by [summ] ascending - their IDs stick to the row?

Any help is much appreciated!

 

[Osvaldo Palmeiro]

Hi. Maybe a macro could do the job.
Paste a copy of the code below to the sheet module (right click on sheet tab | View Code).

Private Sub Worksheet_Change(ByVal Target As Range)
 If Target.Count > 1 Then Exit Sub
 If Target.Column <> 2 Or Target.Value = "" Then Exit Sub
 If Target.Offset(, -1).Value <> "" Then Exit Sub
 Target.Offset(, -1).Value = Application.Max(Columns(1)) + 1
End Sub

How it should work - after you manually insert content in any cell of column B and if the corresponding cell in A is empty, then the code will insert the next ID number in A.