SELECT 
  p.product_id, 
  ifnull(
    count(dp.post_id), 
    0
  ) as discussion_amount_posts 
FROM 
  cscart_discussion 
  INNER JOIN cscart_products as p ON (
    cscart_discussion.object_id = p.product_id
  ) 
  INNER JOIN cscart_discussion_posts as dp ON (
    cscart_discussion.thread_id = dp.thread_id 
    AND cscart_discussion.object_type = 'P' 
    AND cscart_discussion.company_id = 1
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    84, 109, 118, 19, 131, 146, 13, 61, 95, 
    15, 9, 85, 59, 111, 144, 60, 123, 145, 
    113, 6, 14, 63, 136, 50984, 127, 134, 
    42, 50985, 50986, 50988, 50993, 50992
  ) 
GROUP BY 
  p.product_id

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}