Counts of how many Pokémon there are of each dual-type combo, as of US/UM; alt forms are counted separately when they have different types, but not double-counted when they have the same type.

combo-counts.txt

 count |   type   |   type   
-------+----------+----------
    26 | normal   | flying
    14 | grass    | poison
    14 | flying   | bug
    12 | poison   | bug
    10 | water    | rock
     9 | water    | ground
     9 | ground   | rock
     8 | psychic  | steel
     7 | water    | flying
     7 | grass    | flying
     7 | flying   | psychic
     7 | rock     | steel
     6 | fire     | fighting
     6 | fire     | flying
     6 | water    | ice
     6 | water    | poison
     6 | grass    | bug
     6 | grass    | ghost
     6 | ground   | dragon
     6 | flying   | dragon
     6 | psychic  | fairy
     6 | bug      | steel
     5 | normal   | fairy
     5 | fire     | ghost
     5 | water    | psychic
     5 | water    | bug
     5 | water    | dark
     5 | grass    | fairy
     5 | electric | flying
     5 | poison   | dark
     5 | flying   | dark
     5 | bug      | rock
     4 | normal   | fighting
     4 | water    | fairy
     4 | electric | bug
     4 | electric | steel
     4 | fighting | psychic
     4 | ground   | ghost
     4 | ground   | steel
     4 | flying   | rock
     4 | dragon   | dark
     3 | normal   | psychic
     3 | fire     | ground
     3 | fire     | psychic
     3 | fire     | dragon
     3 | fire     | dark
     3 | water    | grass
     3 | water    | electric
     3 | grass    | fighting
     3 | grass    | psychic
     3 | grass    | dark
     3 | grass    | steel
     3 | electric | rock
     3 | ice      | ground
     3 | fighting | bug
     3 | fighting | dark
     3 | poison   | flying
     3 | poison   | ghost
     3 | ground   | flying
     3 | ground   | dark
     3 | flying   | ghost
     3 | psychic  | ghost
     3 | psychic  | dragon
     3 | psychic  | dark
     3 | ghost    | steel
     3 | steel    | fairy
     2 | normal   | fire
     2 | normal   | grass
     2 | normal   | electric
     2 | normal   | dark
     2 | fire     | poison
     2 | fire     | bug
     2 | water    | fighting
     2 | water    | ghost
     2 | water    | dragon
     2 | grass    | ice
     2 | grass    | rock
     2 | grass    | dragon
     2 | electric | dragon
     2 | electric | fairy
     2 | ice      | flying
     2 | ice      | psychic
     2 | ice      | rock
     2 | ice      | dark
     2 | ice      | steel
     2 | fighting | poison
     2 | fighting | dragon
     2 | fighting | steel
     2 | poison   | ground
     2 | poison   | dragon
     2 | ground   | psychic
     2 | ground   | bug
     2 | flying   | steel
     2 | flying   | fairy
     2 | psychic  | rock
     2 | bug      | fairy
     2 | rock     | dragon
     2 | rock     | fairy
     2 | ghost    | dark
     2 | dark     | steel
     1 | normal   | water
     1 | normal   | ground
     1 | normal   | dragon
     1 | fire     | water
     1 | fire     | electric
     1 | fire     | rock
     1 | fire     | steel
     1 | water    | steel
     1 | grass    | electric
     1 | grass    | ground
     1 | electric | ice
     1 | electric | ground
     1 | electric | psychic
     1 | electric | ghost
     1 | ice      | fighting
     1 | ice      | ghost
     1 | ice      | dragon
     1 | ice      | fairy
     1 | fighting | flying
     1 | fighting | rock
     1 | fighting | ghost
     1 | poison   | rock
     1 | bug      | ghost
     1 | rock     | dark
     1 | ghost    | dragon
     1 | ghost    | fairy
     1 | dragon   | steel
     1 | dragon   | fairy
(128 rows)

terrible-query.sql

with counts (count, type_1, type_2) as (
    select count(distinct pt1.pokemon_id), pt1.type_id, pt2.type_id
    from pokemon_types pt1
    join pokemon_types pt2 on
        (pt1.pokemon_id, pt1.form_id) = (pt2.pokemon_id, pt2.form_id)
        and pt1.type_id < pt2.type_id
    where pt1.generation_id = 7 and pt2.generation_id = 7
    group by pt1.type_id, pt2.type_id
)

select c.count, t1.identifier "type", t2.identifier "type"
from counts c
join types t1 on c.type_1 = t1.id
join types t2 on c.type_2 = t2.id
order by c.count desc, t1.id asc, t2.id asc;