SELECT 
  p.product_id, 
  ifnull(
    count(dp.post_id), 
    0
  ) as discussion_amount_posts 
FROM 
  q_discussion 
  INNER JOIN q_products as p ON (
    q_discussion.object_id = p.product_id
  ) 
  INNER JOIN q_discussion_posts as dp ON (
    q_discussion.thread_id = dp.thread_id 
    AND q_discussion.object_type = 'P'
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    3024, 3144, 3145, 3146, 3195, 3368, 3369, 
    3370, 3199, 3377, 3378, 3379, 3203, 
    3381, 3382, 3383, 3384, 3385, 3386, 
    3387, 3388, 3389, 3390, 3391, 3392, 
    3393, 3394, 3395, 3396, 3397, 3398, 
    3399, 3400, 3401, 3402, 3403, 3404, 
    3405, 3406, 3407, 3408, 3409, 3410, 
    3411, 3412, 3413, 3414, 3415, 3416, 
    3417, 3418, 3419, 3420, 3421, 3422, 
    3423, 3424, 3248, 3426, 3427, 3428, 
    3429, 3430, 3431, 3432, 3433, 3434, 
    3435, 3436, 3437, 3438, 3439
  ) 
GROUP BY 
  p.product_id

Query time 0.00102

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "21.61"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "0.29"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "dp",
            "access_type": "ALL",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "rows_examined_per_scan": 57,
            "rows_produced_per_join": 5,
            "filtered": "10.00",
            "cost_info": {
              "read_cost": "13.01",
              "eval_cost": "1.14",
              "prefix_cost": "14.15",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "(`portal`.`dp`.`status` = 'A')"
          }
        },
        {
          "table": {
            "table_name": "q_discussion",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "object_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.dp.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "5.70",
              "eval_cost": "0.06",
              "prefix_cost": "20.99",
              "data_read_per_join": "4"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type"
            ],
            "attached_condition": "((`portal`.`q_discussion`.`object_id` in (3024,3144,3145,3146,3195,3368,3369,3370,3199,3377,3378,3379,3203,3381,3382,3383,3384,3385,3386,3387,3388,3389,3390,3391,3392,3393,3394,3395,3396,3397,3398,3399,3400,3401,3402,3403,3404,3405,3406,3407,3408,3409,3410,3411,3412,3413,3414,3415,3416,3417,3418,3419,3420,3421,3422,3423,3424,3248,3426,3427,3428,3429,3430,3431,3432,3433,3434,3435,3436,3437,3438,3439)) and (`portal`.`q_discussion`.`object_type` = 'P'))"
          }
        },
        {
          "table": {
            "table_name": "p",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_discussion.object_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "0.29",
              "eval_cost": "0.06",
              "prefix_cost": "21.33",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id"
            ]
          }
        }
      ]
    }
  }
}