Tohle by mělo stačit... group by a group_concat
select
pr.project_id,
pr.team_size,
pr.from_date,
GROUP_CONCAT(tech.technology_name separator ', ') as technologies
from
project pr
JOIN project_technologies ptech ON pr.project_id=ptech.project_id
JOIN technologies tl ON ptech.technology_id=tl.technology_id
GROUP BY
pr.project_id,
pr.team_size,
pr.from_date
EDIT opraveno, aby zahrnovalo klauzuli JOIN