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 (
    98955, 98956, 98957, 98958, 98959, 98960, 
    98961, 98962, 98963, 98964, 98965, 
    98966, 98967, 98968, 98969, 98970, 
    98971, 98972, 98973, 98974, 98975, 
    98976, 98977, 98978, 98979, 98980, 
    98981, 98982, 98983, 98984, 98985, 
    98986, 98987, 98988, 98989, 98990, 
    98991, 98992, 98993, 98994, 98995, 
    98996, 98997, 98998, 98999, 99000, 
    99001, 99002, 99003, 99004, 99005, 
    99006, 99007, 99008, 99009, 99010, 
    99011, 99056, 99057, 99058, 99059, 
    99060, 99061, 99062, 99063, 99064, 
    99065, 99066, 99067, 99133, 99141, 
    99142, 99151, 99152, 99169, 99170, 
    99248, 99257, 99262, 99322, 99323, 
    99324, 99325, 99326, 99327, 99328, 
    99329, 99333, 99334, 99335, 99336, 
    99337, 99338, 99339, 99340, 99341
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00126

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 (98955,98956,98957,98958,98959,98960,98961,98962,98963,98964,98965,98966,98967,98968,98969,98970,98971,98972,98973,98974,98975,98976,98977,98978,98979,98980,98981,98982,98983,98984,98985,98986,98987,98988,98989,98990,98991,98992,98993,98994,98995,98996,98997,98998,98999,99000,99001,99002,99003,99004,99005,99006,99007,99008,99009,99010,99011,99056,99057,99058,99059,99060,99061,99062,99063,99064,99065,99066,99067,99133,99141,99142,99151,99152,99169,99170,99248,99257,99262,99322,99323,99324,99325,99326,99327,99328,99329,99333,99334,99335,99336,99337,99338,99339,99340,99341)) 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)"
          }
        }
      ]
    }
  }
}