Вам же группировка по дате нужна? Используйте функцию DATE
"The DATE() function extracts the date part from a datetime expression."
SELECT COUNT(id) AS cnt, DATE(closed_on) AS closed_on, issues.status_id
FROM issues
WHERE closed_on IS NOT NULL AND closed_on <= '#{end_from_created_date}'
AND created_on <= '#{end_from_created_date}'
GROUP BY DATE(closed_on), status_id
