Postgres GROUP BY on jsonb inner field

Question

I am using Postgresql 9.4 and have a table test, with id::int and content::jsonb, as follows:

Answer 1

I think json_agg() is not the best choice to use it here, since that is concatenating the content values (the whole json data) into an array for a specific group.
It makes more sense to use something like this (and I added 'count(*)', just to have a more common scenario):

SELECT content #>> '{a,b}' as a_b, count(*) as count FROM test GROUP BY content #>> '{a,b}';