gistfile1.rb

Item.joins("LEFT JOIN comments ON comments.item_id=items.id AND comments.service='TRUE'")
	.joins("LEFT JOIN comments c2 ON c2.item_id=items.id AND c2.service='TRUE' AND (COALESCE(c2.created_at, items.purchased_at) + INTERVAL items.service_interval YEAR) >= NOW() AND c2.id <> comments.id")
	.where("(COALESCE(comments.created_at, items.purchased_at) + INTERVAL items.service_interval YEAR) < NOW()")
	.where("c2.id IS NULL")
	.where("items.service_interval IS NOT NULL AND items.service_interval > 0")


Item.joins("LEFT JOIN comments ON comments.item_id=items.id AND comments.service='TRUE'")
	.joins("LEFT JOIN comments c2 ON c2.item_id=items.id AND c2.service='TRUE' AND (COALESCE(c2.created_at, items.created_at) + INTERVAL items.service_interval) >= NOW()")
	.where("(COALESCE(comments.created_at, items.created_at) + items.service_interval) < NOW()")
	.where("c2.id IS NULL")
	.where("items.service_interval IS NOT NULL AND items.service_interval > 0")

Item.joins("LEFT JOIN comments ON comments.item_id=items.id AND comments.service='TRUE'")
  .where("(COALESCE(comments.created_at, items.created_at) + items.service_interval) < NOW()")
  .where("items.service_interval IS NOT NULL AND items.service_interval > 0")

# Item.joins(:comments)
# 	.where(comments: {service: true})
# 	.where("(comments.created_at + items.service_interval) < NOW()")