I have a Postgres table and I want to output its contents as JSON so I can have a .json file for some tests. Turns out, this is pretty easy. Let's say the table name is users:

select array_to_json(array_agg(row_to_json(t)))
from (
) t

And done. That will output the entire users table (everything that matches the SELECT query) to a JSON array that you can just drop into a file.