count rows with group by and having count (postgres)

Hi I’m having trouble with query in PostgreSQL . Here is example data from my table imgs_tags :

img_id | tag_id
   1        2
   1        3
   2        2
   2        3
   3        2
   3        3

I had tried :

select count(img_id) from imgs_tags where tag_id IN(2,3) group by img_id having count(tag_id) = 2

and it returns as below :

count:
  2
  2 
  2

But I want it to return count = 3 . How can i fix it ? Thanks

Answer

You should write like this:

select count(*) from (
select img_id
from imgs_tags 
where tag_id IN (2,3) 
group by img_id
having count(tag_id) = 2
) t

or if you want to do some further operation with this data then better use Common Table Expression (with clause) like below:

with cte as (
select img_id
from imgs_tags 
where tag_id IN (2,3) 
group by img_id
having count(tag_id) = 2
) 

select count(*) from cte