gistfile1.sql

SELECT leads.id, 
  (SELECT COUNT(*) FROM searches WHERE lead_id = leads.id) AS searches_count,
  (SELECT COUNT(*) FROM rental_searches WHERE lead_id = leads.id) AS rental_searches_count,
  COALESCE((searches_count + rental_searches_count), 0) as total
FROM leads
WHERE leads.id = 35



#   Unknown column 'searches_count' in 'field list'

SELECT leads.id,
(SELECT COUNT() FROM searches WHERE lead_id = 35) AS searches_count,
(SELECT COUNT() FROM rental_searches WHERE lead_id = 35) AS rental_searches_count,
COALESCE((searches_count + rental_searches_count), 0) as total
FROM leads
WHERE leads.id = 35

If you're really doing only running this query at any one time for a specific lead.id then it's probably better to just specify the id in the sub-queries. Also, make sure you have indexes on lead_id on the searches and rental_searches table.