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 (
    100579, 100580, 100581, 100582, 100583, 
    100584, 100585, 100586, 100587, 100588, 
    100589, 100590, 100591, 100592, 100593, 
    101047, 101048, 101049, 101050, 101051, 
    101052, 101053, 101574, 101575, 101576, 
    101577, 101578, 101579, 101580, 101581, 
    101582, 101583, 101584, 101585, 101586, 
    101587, 101588, 101589, 101590, 101591, 
    101592, 101593, 101594, 101595, 101596, 
    101597, 101598, 101599, 101600, 101601, 
    101602, 101603, 101604, 101605, 101606, 
    101607, 101608, 101609, 101610, 101611, 
    101612, 101613, 101614, 101615, 101616, 
    101617, 101618, 101619, 101620, 101621, 
    101622, 101623, 101624
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00143

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "84.21"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "range",
            "possible_keys": [
              "object_id"
            ],
            "key": "object_id",
            "used_key_parts": [
              "object_id",
              "object_type"
            ],
            "key_length": "6",
            "rows_examined_per_scan": 73,
            "rows_produced_per_join": 73,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (100579,100580,100581,100582,100583,100584,100585,100586,100587,100588,100589,100590,100591,100592,100593,101047,101048,101049,101050,101051,101052,101053,101574,101575,101576,101577,101578,101579,101580,101581,101582,101583,101584,101585,101586,101587,101588,101589,101590,101591,101592,101593,101594,101595,101596,101597,101598,101599,101600,101601,101602,101603,101604,101605,101606,101607,101608,101609,101610,101611,101612,101613,101614,101615,101616,101617,101618,101619,101620,101621,101622,101623,101624)) and (`nuie_scalesta_net`.`cscart_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "43.81",
              "eval_cost": "7.30",
              "prefix_cost": "51.11",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        },
        {
          "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": [
              "nuie_scalesta_net.cscart_discussion.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 73,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "18.25",
              "eval_cost": "7.30",
              "prefix_cost": "76.66",
              "data_read_per_join": "31K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_posts), (`nuie_scalesta_net`.`cscart_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 73,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "7.30",
              "prefix_cost": "84.21",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_discussion_rating), ((`nuie_scalesta_net`.`cscart_discussion_rating`.`post_id` = `nuie_scalesta_net`.`cscart_discussion_posts`.`post_id`) and (`nuie_scalesta_net`.`cscart_discussion_rating`.`thread_id` = `nuie_scalesta_net`.`cscart_discussion`.`thread_id`) and (`nuie_scalesta_net`.`cscart_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}