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 (
    93575, 93576, 93577, 93578, 93579, 93580, 
    93581, 93582, 93583, 93584, 93585, 
    93586, 93587, 93588, 93589, 93590, 
    93591, 93592, 93593, 93594, 93595, 
    93596, 93597, 93598, 93599, 93600, 
    93601, 93602, 93603, 93604, 93605, 
    93606, 93607, 93608, 93609, 93610, 
    93611, 93612, 93613, 93614, 93615, 
    93616, 93617, 93618, 93619, 93620, 
    93621, 93622, 93623, 93624, 93625, 
    93626, 93627, 93628, 93629, 93630, 
    93631, 93632, 93633, 93634, 93635, 
    93636, 93637, 93638, 93639, 93640, 
    93641, 93642, 93643, 93644, 93645, 
    93646, 93647, 93648, 93649, 93650, 
    93651, 93652, 93653, 93654, 93655, 
    93656, 93657, 93658, 93659, 93660, 
    93661, 93662, 93663, 93664, 93665, 
    93666, 93667, 93668, 93669, 93670
  ) 
  AND cscart_discussion.object_type = "P" 
GROUP BY 
  cscart_discussion.object_id

Query time 0.00135

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 (93575,93576,93577,93578,93579,93580,93581,93582,93583,93584,93585,93586,93587,93588,93589,93590,93591,93592,93593,93594,93595,93596,93597,93598,93599,93600,93601,93602,93603,93604,93605,93606,93607,93608,93609,93610,93611,93612,93613,93614,93615,93616,93617,93618,93619,93620,93621,93622,93623,93624,93625,93626,93627,93628,93629,93630,93631,93632,93633,93634,93635,93636,93637,93638,93639,93640,93641,93642,93643,93644,93645,93646,93647,93648,93649,93650,93651,93652,93653,93654,93655,93656,93657,93658,93659,93660,93661,93662,93663,93664,93665,93666,93667,93668,93669,93670)) 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",
            "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": 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), (`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": 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)"
          }
        }
      ]
    }
  }
}