SELECT 
  cscart_discussion.object_id AS product_id, 
  AVG(
    cscart_discussion_rating.rating_value
  ) AS average_rating, 
  cscart_discussion.type AS discussion_type, 
  cscart_discussion.thread_id AS discussion_thread_id 
FROM 
  cscart_discussion 
  LEFT JOIN cscart_discussion_posts ON cscart_discussion_posts.thread_id = cscart_discussion.thread_id 
  AND cscart_discussion_posts.status = "A" 
  LEFT JOIN cscart_discussion_rating ON cscart_discussion.thread_id = cscart_discussion_rating.thread_id 
  AND cscart_discussion_rating.post_id = cscart_discussion_posts.post_id 
  AND cscart_discussion_rating.rating_value != 0 
WHERE 
  cscart_discussion.object_id IN (
    4418, 4421, 4420, 4423, 4600, 5961, 5960, 
    5958, 5959, 1773, 3665, 3666, 4625, 
    5065, 3654, 2237, 3435, 1486, 1083, 
    1231, 1485, 2238, 3427, 3437, 3502, 
    3501, 3436, 7751, 6072, 5603, 6710, 
    4839, 4838, 7593, 7594, 7595, 7596, 
    7597, 7598, 7599, 7600, 6413, 6412, 
    6414, 6415, 6419, 6420, 6418, 6417, 
    6416, 5607, 5605, 5606, 5699, 5703, 
    5701, 5700, 5697, 5702, 5698, 7249, 
    7247, 7243, 7248, 7246, 7244, 7242, 
    7245, 6692, 6702, 6703, 6704, 6705, 
    6707, 6708, 6706, 5704, 1297, 1301, 
    1298, 1299, 1296, 1294, 1300, 1295, 
    3576, 3585, 3584, 3575, 7601, 7602, 
    6709, 3146, 3752, 3145, 5096
  ) 
  AND cscart_discussion.object_type = "P" 
  AND cscart_discussion.company_id = 1 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00143

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "134.41"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "range",
            "possible_keys": [
              "object_id",
              "company_id"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type",
              "company_id"
            ],
            "key_length": "10",
            "rows_examined_per_scan": 96,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "index_condition": "((`dbggbern`.`cscart_discussion`.`company_id` = 1) and (`dbggbern`.`cscart_discussion`.`object_id` in (4418,4421,4420,4423,4600,5961,5960,5958,5959,1773,3665,3666,4625,5065,3654,2237,3435,1486,1083,1231,1485,2238,3427,3437,3502,3501,3436,7751,6072,5603,6710,4839,4838,7593,7594,7595,7596,7597,7598,7599,7600,6413,6412,6414,6415,6419,6420,6418,6417,6416,5607,5605,5606,5699,5703,5701,5700,5697,5702,5698,7249,7247,7243,7248,7246,7244,7242,7245,6692,6702,6703,6704,6705,6707,6708,6706,5704,1297,1301,1298,1299,1296,1294,1300,1295,3576,3585,3584,3575,7601,7602,6709,3146,3752,3145,5096)) and (`dbggbern`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "57.61",
              "eval_cost": "9.60",
              "prefix_cost": "67.21",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type",
              "company_id"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_posts",
            "access_type": "ref",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "dbggbern.cscart_discussion.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "24.00",
              "eval_cost": "9.60",
              "prefix_cost": "100.81",
              "data_read_per_join": "42K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_posts), (`dbggbern`.`cscart_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "post_id"
            ],
            "key_length": "3",
            "ref": [
              "dbggbern.cscart_discussion_posts.post_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "24.00",
              "eval_cost": "9.60",
              "prefix_cost": "134.41",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_rating), ((`dbggbern`.`cscart_discussion_rating`.`thread_id` = `dbggbern`.`cscart_discussion`.`thread_id`) and (`dbggbern`.`cscart_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}