Show the ids and details for all projects.
select project_id, project_details from projects
For each of them, also show the number of documents.
select t1.project_id, t1.project_details, count(*) from projects as t1 join documents as t2 on t1.project_id = t2.project_id group by t1.project_id
Which of them have at least two documents?
select t1.project_id, t1.project_details from projects as t1 join documents as t2 on t1.project_id = t2.project_id group by t1.project_id having count(*) > 2