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 (
    51567, 51565, 51564, 139, 129, 51566, 
    51301, 51, 50, 51497, 51498, 53, 22713, 
    21, 22714, 22712, 46, 22715, 22716, 
    51496, 21567, 91, 50989, 47, 105, 48, 
    49, 92, 137, 88, 126, 31, 51358, 115, 
    37, 11, 140, 41, 30, 90, 38, 124, 81, 56, 
    135, 82, 116, 117, 125, 106, 39, 193, 
    65, 40, 22710, 22711, 17, 57, 122, 58, 
    5, 22, 18, 27
  ) 
GROUP BY 
  p.product_id

Query time 0.00054

JSON explain

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