How many minifigs have unique heads?

Question

Most minifig heads seem to be shared by a few designs, but Alex's answer to a minifig identification question left me wondering: how many minifigs have heads that are unique to them? Presumably you're talking about a unique, widely recognizable character. Or a more precise way to put it: how many (and which) minifig heads have only one minifigure associated with them from official sets? And I think we should limit the set of minifig heads to those that bricklink calls "Minifigure, Head" and leave out "Minifigure, Head, Modified".

I'm guessing most of these are going to be for Star Wars or other licensed themes, but I'm hoping someone can find a good way to come up with an answer that lists the examples or show how to do a bricklink query to determine the answer. If the list is included here it would only be complete at this point in time, but that would still be cool to see.

Answer 1

There are 2,140 heads that have only been included in one minifig based on the current Rebrickable database. I generated the full list of all heads (as of March 28, 2022) including the unique number of minifigs they have been used in.

For those who are curious or want to explore this in a different way, here's the query I used:

select
  count(1),
  part_num,
  color_id,
  name
from
  inventories
  join inventory_parts on inventories.id = inventory_parts.inventory_id
  natural join parts
where
  set_num like 'fig%'
  and (
    part_num like '24581%'
    or part_num like '33464%'
    or part_num like '3626%'
  )
group by
  part_num,
  color_id
order by
  count(1) desc;

It's worth noting that "unique" here is based on the mold, print, and color combination used by Rebrickable. A minifig head with the same color and print but different mold (often open/blocked/closed stud) will count as a unique head in this query.