How to discard some fields to make count?

[#1]

Hi Everybody

I have a table like this:

ID	ID Padre
IM23456
IM26788
IM74777	IM78789
IM34677
IM98789
IM44323	IM98767

The idea is to count and show in a graphic only the elements in ID field that don´t have any data in ID Padre field, for the example would be 4 ID because i have 2 Items with data in ID Padre field.

How can i make this?

[johnw · Accepted solution]

Maybe this?

count(if(len("ID Padre")=0,ID))

[#3]

!Thanks for your great help¡