query5.sql

SELECT SUM(NOW()::date - sq.sig) FROM(
SELECT DISTINCT programmers.id, programmers.signed_in_at AS sig 
FROM programmers
INNER JOIN projects_programmers ON (programmers.id = projects_programmers.programmer_id)
INNER JOIN projects ON (projects_programmers.project_id = projects.id)
INNER JOIN languages ON (languages.id = projects.language_id)
WHERE languages.label LIKE 'ruby') AS sq;