Get IMC statistics for intervals to measure performance

intervals

SELECT AVG(days_diff) AS avg_days, MIN(days_diff) AS min_days, MAX(days_diff) AS max_days, COUNT(issueid) AS count_issues,stepid, s.title AS steptitle, s.stepcolor,catid, c.title AS category
FROM 
			(
				SELECT DISTINCT * FROM (

					SELECT a.issueid, a.stepid, b.catid, a.created,
					  CASE WHEN (a.created - f.created) IS NULL THEN a.created + INTERVAL 1 SECOND ELSE f.created END AS vcreated,
					  CASE WHEN (a.created - f.created) IS NULL THEN 0 ELSE ABS(DATEDIFF(a.created, f.created)) END AS days_diff

					FROM scsue_imc_log AS a
					  LEFT JOIN scsue_imc_log AS f ON a.created > f.created AND a.issueid = f.issueid
					  LEFT JOIN scsue_imc_issues AS b ON b.id = a.issueid
					WHERE a.issueid IN (
					  SELECT id
					  FROM scsue_imc_issues AS p
					  WHERE p.state = 1
					  AND p.stepid <> 1
					)
					AND a.action = "step"
					AND a.state = 1
					GROUP BY vcreated

				) AS dis
				GROUP BY issueid

			) AS intervals
		
LEFT JOIN scsue_imc_steps AS s ON s.id = intervals.stepid
LEFT JOIN scsue_categories AS c ON c.id = intervals.catid
GROUP BY catid, stepid