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 (
    908, 
    134, 
    919, 
    918, 
    924, 
    922, 
    921, 
    925, 
    525, 
    917, 
    916, 
    955, 
    942, 
    941, 
    446, 
    953, 
    952, 
    951, 
    949, 
    948, 
    947, 
    946, 
    945, 
    944, 
    982, 
    980, 
    979, 
    978, 
    981, 
    478, 
    977, 
    975, 
    974, 
    973, 
    972, 
    971, 
    970, 
    994, 
    996, 
    493, 
    985, 
    986, 
    988, 
    990, 
    991, 
    993, 
    1254, 
    1253, 
    247, 
    1274, 
    1483, 
    1484, 
    1485, 
    1486, 
    1487, 
    2478, 
    2483, 
    2482, 
    2484, 
    2485, 
    2486, 
    2487, 
    2488, 
    2489, 
    8422, 
    2574, 
    3754, 
    3755, 
    3756, 
    3757, 
    3758, 
    3759, 
    3760, 
    3761, 
    3762, 
    3764, 
    3765, 
    1930, 
    3815, 
    3817, 
    3818, 
    4432, 
    4438, 
    4440, 
    4441, 
    4442, 
    4443, 
    4444, 
    4448, 
    4445, 
    4446, 
    4447, 
    6149, 
    5685, 
    6148, 
    6150, 
    6151, 
    5727, 
    5729, 
    5730, 
    5731, 
    5732, 
    5733, 
    5734, 
    5735, 
    5736, 
    5739, 
    5741, 
    5742, 
    5743, 
    5744, 
    5745, 
    5746, 
    5747, 
    5748, 
    5749, 
    5750, 
    5752, 
    5753, 
    5754, 
    5755, 
    5756, 
    5757, 
    5758, 
    5759, 
    5760, 
    5761, 
    5762, 
    7004, 
    7005, 
    7006, 
    7007, 
    7008, 
    7009, 
    7010, 
    7011, 
    7012, 
    7013, 
    7014, 
    7015, 
    10284, 
    10285, 
    10286, 
    10287, 
    10288, 
    10289, 
    10290, 
    10291, 
    10292, 
    10293
  ) 
GROUP BY 
  p.product_id

Query time 0.00117

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 (908,134,919,918,924,922,921,925,525,917,916,955,942,941,446,953,952,951,949,948,947,946,945,944,982,980,979,978,981,478,977,975,974,973,972,971,970,994,996,493,985,986,988,990,991,993,1254,1253,247,1274,1483,1484,1485,1486,1487,2478,2483,2482,2484,2485,2486,2487,2488,2489,8422,2574,3754,3755,3756,3757,3758,3759,3760,3761,3762,3764,3765,1930,3815,3817,3818,4432,4438,4440,4441,4442,4443,4444,4448,4445,4446,4447,6149,5685,6148,6150,6151,5727,5729,5730,5731,5732,5733,5734,5735,5736,5739,5741,5742,5743,5744,5745,5746,5747,5748,5749,5750,5752,5753,5754,5755,5756,5757,5758,5759,5760,5761,5762,7004,7005,7006,7007,7008,7009,7010,7011,7012,7013,7014,7015,10284,10285,10286,10287,10288,10289,10290,10291,10292,10293)) 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"
            ]
          }
        }
      ]
    }
  }
}