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'
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    2227, 
    2226, 
    2430, 
    2431, 
    2522, 
    2655, 
    2698, 
    2702, 
    2703, 
    2719, 
    2728, 
    2805, 
    2808, 
    2922, 
    2923, 
    2924, 
    2925, 
    3112, 
    3113, 
    3114, 
    3115, 
    3150, 
    3151, 
    3153, 
    3155, 
    3156, 
    3213, 
    3214, 
    3216, 
    3215, 
    2737, 
    3255, 
    3289, 
    3377, 
    3378, 
    3382, 
    3383, 
    3385, 
    3386, 
    3552, 
    3553, 
    3604, 
    3603, 
    3605, 
    3606, 
    3664, 
    3665, 
    3832, 
    3831, 
    3834, 
    3835, 
    4024, 
    3649, 
    4026, 
    4025, 
    4110, 
    4111, 
    3811, 
    4899, 
    4898, 
    4897, 
    4896, 
    4894, 
    4915, 
    4917, 
    4924, 
    4923, 
    4922, 
    4921, 
    4920, 
    4919, 
    4918, 
    4925, 
    4927, 
    4926, 
    4944, 
    4942, 
    4945, 
    4951, 
    4953, 
    4959, 
    4958, 
    4973, 
    4972, 
    4971, 
    4970, 
    4969, 
    4968, 
    4967, 
    4966, 
    4965, 
    4964, 
    4963, 
    4962, 
    4987, 
    4986, 
    4985, 
    4984, 
    4977, 
    4976, 
    4981, 
    4980, 
    4979, 
    4978, 
    4982, 
    4983, 
    5117, 
    5116, 
    5114, 
    5618, 
    5619, 
    5620, 
    5621, 
    6149, 
    5685, 
    6148, 
    6150, 
    6151, 
    5687, 
    5688, 
    5689, 
    5690, 
    5691, 
    5692, 
    5693, 
    5694, 
    5696, 
    5697, 
    5698, 
    5699, 
    5703, 
    5704, 
    5705, 
    5721, 
    5722, 
    5723, 
    5724, 
    5725, 
    5726, 
    5894, 
    5893, 
    5892, 
    5934, 
    5935, 
    5944, 
    5945, 
    5946, 
    5947, 
    6119, 
    6120, 
    6121, 
    6122, 
    6123, 
    6124, 
    6125, 
    5948, 
    6128, 
    6127, 
    6126, 
    6129, 
    6130, 
    6131, 
    6132, 
    6133, 
    6134, 
    6135, 
    6026, 
    6025, 
    6027, 
    6028, 
    6029, 
    6030, 
    6041, 
    6042, 
    6043, 
    6044, 
    6045, 
    6046, 
    6047, 
    6054, 
    6055, 
    6056, 
    6057, 
    6058, 
    6059, 
    5956, 
    6087, 
    6088, 
    6089, 
    6090, 
    6091, 
    6092, 
    6093, 
    6098, 
    6100, 
    5683, 
    6152, 
    6153, 
    6154, 
    6155, 
    6196, 
    6195, 
    6194, 
    6197, 
    6198, 
    6199, 
    6200, 
    6201, 
    6202
  ) 
GROUP BY 
  p.product_id

Query time 0.00125

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.31"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "dp",
            "access_type": "ALL",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "rows_examined_per_scan": 13,
            "rows_produced_per_join": 1,
            "filtered": "10.00",
            "cost_info": {
              "read_cost": "1.70",
              "eval_cost": "0.13",
              "prefix_cost": "1.83",
              "data_read_per_join": "582"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`dp`.`status` = 'A')"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "object_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "softwarepirmam_hewadelivard_cscart_4.dp.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "0.33",
              "eval_cost": "0.01",
              "prefix_cost": "2.28",
              "data_read_per_join": "1"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type"
            ],
            "attached_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_discussion`.`object_id` in (2227,2226,2430,2431,2522,2655,2698,2702,2703,2719,2728,2805,2808,2922,2923,2924,2925,3112,3113,3114,3115,3150,3151,3153,3155,3156,3213,3214,3216,3215,2737,3255,3289,3377,3378,3382,3383,3385,3386,3552,3553,3604,3603,3605,3606,3664,3665,3832,3831,3834,3835,4024,3649,4026,4025,4110,4111,3811,4899,4898,4897,4896,4894,4915,4917,4924,4923,4922,4921,4920,4919,4918,4925,4927,4926,4944,4942,4945,4951,4953,4959,4958,4973,4972,4971,4970,4969,4968,4967,4966,4965,4964,4963,4962,4987,4986,4985,4984,4977,4976,4981,4980,4979,4978,4982,4983,5117,5116,5114,5618,5619,5620,5621,6149,5685,6148,6150,6151,5687,5688,5689,5690,5691,5692,5693,5694,5696,5697,5698,5699,5703,5704,5705,5721,5722,5723,5724,5725,5726,5894,5893,5892,5934,5935,5944,5945,5946,5947,6119,6120,6121,6122,6123,6124,6125,5948,6128,6127,6126,6129,6130,6131,6132,6133,6134,6135,6026,6025,6027,6028,6029,6030,6041,6042,6043,6044,6045,6046,6047,6054,6055,6056,6057,6058,6059,5956,6087,6088,6089,6090,6091,6092,6093,6098,6100,5683,6152,6153,6154,6155,6196,6195,6194,6197,6198,6199,6200,6201,6202)) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_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": [
              "softwarepirmam_hewadelivard_cscart_4.cscart_discussion.object_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "0.02",
              "eval_cost": "0.01",
              "prefix_cost": "2.31",
              "data_read_per_join": "294"
            },
            "used_columns": [
              "product_id"
            ]
          }
        }
      ]
    }
  }
}