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 (
    22151, 21355, 21300, 22160, 20221, 21345, 
    21488, 21356, 21301, 22161, 20222, 
    21346, 22153, 21357, 21302, 21552, 
    20223, 21347, 21292, 22154, 21303, 
    21553, 21514, 21348, 21293, 22155, 
    21304, 21286, 21349, 21294, 22156, 
    21305, 21290, 21350, 21295, 22157, 
    21306, 21291, 21351, 21296, 22158, 
    21307, 21287, 21352, 21297, 22159, 
    21342, 21288, 21353, 21298, 22175, 
    21343, 21289, 21354, 21299, 22177, 
    22152, 21344
  ) 
GROUP BY 
  p.product_id

Query time 0.00198

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "p",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 58,
          "filtered": 100,
          "attached_condition": "p.product_id in (22151,21355,21300,22160,20221,21345,21488,21356,21301,22161,20222,21346,22153,21357,21302,21552,20223,21347,21292,22154,21303,21553,21514,21348,21293,22155,21304,21286,21349,21294,22156,21305,21290,21350,21295,22157,21306,21291,21351,21296,22158,21307,21287,21352,21297,22159,21342,21288,21353,21298,22175,21343,21289,21354,21299,22177,22152,21344)",
          "using_index": true
        }
      },
      {
        "table": {
          "table_name": "cscart_discussion",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "object_id", "idx_company_id"],
          "key": "object_id",
          "key_length": "10",
          "used_key_parts": ["object_id", "object_type", "company_id"],
          "ref": ["lillyshop_lillyshop.p.product_id", "const", "const"],
          "rows": 1,
          "filtered": 100,
          "index_condition": "cscart_discussion.object_type = 'P'"
        }
      },
      {
        "table": {
          "table_name": "dp",
          "access_type": "ref",
          "possible_keys": ["thread_id", "thread_id_2"],
          "key": "thread_id_2",
          "key_length": "6",
          "used_key_parts": ["thread_id", "status"],
          "ref": ["lillyshop_lillyshop.cscart_discussion.thread_id", "const"],
          "rows": 2,
          "filtered": 100,
          "index_condition": "dp.`status` = 'A'"
        }
      }
    ]
  }
}