Re: Syntax error needs explanation

The current version of the script:

select c.company_nbr, c.company_name, c.industry
from companies as c
where exists (
   select e.company_nbr
   from enforcement as e
   )
group by c.industry
order by c.industry;

And psql tells me that c.company_nbr must be in the group by clause.
However, when I do that the output is a list of company numbers and names in
each industry.

My web searches on using the exists operator haven't provided the knowlege
for me to use it properly.