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 (
    93465, 93466, 93467, 93468, 93469, 93470, 
    93471, 93472, 93473, 93474, 93475, 
    93476, 93477, 93478, 93479, 93480, 
    93481, 93482, 93483, 93484, 93485, 
    93486, 93487, 93488, 93489, 93490, 
    93491, 93492, 93493, 93494, 93495, 
    93496, 93497, 93498, 93499, 93500, 
    93501, 93502, 93503, 93504, 93505, 
    93506, 93507, 93508, 93509, 93510, 
    93511, 93512, 93513, 93514, 93529, 
    93530, 93531, 93532, 93533, 93534, 
    93535, 93536, 93537, 93538, 93539, 
    93540, 93541, 93542, 93543, 93544, 
    93545, 93546, 93547, 93548, 93549, 
    93550, 93551, 93552, 93553, 93554, 
    93555, 93556, 93557, 93558, 93559, 
    93560, 93561, 93562, 93563, 93564, 
    93565, 93566, 93567, 93568, 93569, 
    93570, 93571, 93572, 93573, 93574
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00139

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "110.66"
    },
    "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": 96,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "index_condition": "((`nuie_scalesta_net`.`cscart_discussion`.`object_id` in (93465,93466,93467,93468,93469,93470,93471,93472,93473,93474,93475,93476,93477,93478,93479,93480,93481,93482,93483,93484,93485,93486,93487,93488,93489,93490,93491,93492,93493,93494,93495,93496,93497,93498,93499,93500,93501,93502,93503,93504,93505,93506,93507,93508,93509,93510,93511,93512,93513,93514,93529,93530,93531,93532,93533,93534,93535,93536,93537,93538,93539,93540,93541,93542,93543,93544,93545,93546,93547,93548,93549,93550,93551,93552,93553,93554,93555,93556,93557,93558,93559,93560,93561,93562,93563,93564,93565,93566,93567,93568,93569,93570,93571,93572,93573,93574)) and (`nuie_scalesta_net`.`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"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_posts",
            "access_type": "ref",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id_2",
            "used_key_parts": [
              "thread_id",
              "status"
            ],
            "key_length": "6",
            "ref": [
              "nuie_scalesta_net.cscart_discussion.thread_id",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "using_index": true,
            "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"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion_rating",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 96,
            "filtered": "100.00",
            "using_join_buffer": "hash join",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "9.60",
              "prefix_cost": "110.66",
              "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)"
          }
        }
      ]
    }
  }
}