orphaned_ateo_selection.sql

-- little slower
WITH linked_outputs AS (
  SELECT templates.id AS id FROM (
    SELECT DISTINCT(template_output) AS id
      FROM action_trigger.event WHERE template_output IS NOT NULL
    UNION
    SELECT DISTINCT(error_output) AS id
      FROM action_trigger.event WHERE error_output IS NOT NULL
    UNION
    SELECT DISTINCT(async_output) AS id
      FROM action_trigger.event WHERE async_output IS NOT NULL
  ) templates
)
SELECT id FROM action_trigger.event_output WHERE id NOT IN (SELECT id FROM linked_outputs);

-- little faster
SELECT ateo.id
FROM action_trigger.event_output AS ateo
WHERE NOT EXISTS (SELECT 1 FROM action_trigger.event WHERE template_output = ateo.id)
  AND NOT EXISTS (SELECT 1 FROM action_trigger.event WHERE error_output = ateo.id)
  AND NOT EXISTS (SELECT 1 FROM action_trigger.event WHERE async_output = ateo.id);

-- very slow!
SELECT ateo.id
FROM action_trigger.event_output AS ateo
LEFT JOIN action_trigger.event AS ate ON (
        ateo.id = ate.template_output
        OR ateo.id = ate.error_output
        OR ateo.id = ate.async_output
)
WHERE ate IS NULL;