/* original query
WITH times AS (
  SELECT id, submitted_at AS time, 1 AS adj FROM jobs
  UNION
  SELECT id, finished_at, -1 FROM jobs
  ORDER BY 2 LIMIT 50
)
SELECT id, time, adj, SUM(adj) OVER (ORDER BY time) FROM times;
*/

SELECT
j.id,
COUNT(j2.*)
FROM
jobs j
LEFT OUTER JOIN jobs j2 ON j2.submitted_at BETWEEN j.submitted_at AND j.finished_at
HAVING
COUNT(j2.*) > 300