SELECT 
  q_discussion.object_id AS product_id, 
  AVG(
    q_discussion_rating.rating_value
  ) AS average_rating, 
  q_discussion.type AS discussion_type, 
  q_discussion.thread_id AS discussion_thread_id 
FROM 
  q_discussion 
  LEFT JOIN q_discussion_posts ON q_discussion_posts.thread_id = q_discussion.thread_id 
  AND q_discussion_posts.status = "A" 
  LEFT JOIN q_discussion_rating ON q_discussion.thread_id = q_discussion_rating.thread_id 
  AND q_discussion_rating.post_id = q_discussion_posts.post_id 
  AND q_discussion_rating.rating_value != 0 
WHERE 
  q_discussion.object_id IN (
    30281, 30282, 30283, 30284, 30285, 30286, 
    30287, 30288, 30289, 30290, 30291, 
    30292, 30293, 30294, 30295, 30296, 
    30297, 30298, 30299, 30300, 30301, 
    30302, 30303, 30304, 30305, 30306, 
    30307, 30309, 30310, 30311, 30312, 
    30313, 30314, 30315, 30316, 30317, 
    30318, 30320, 30321, 30322, 30323, 
    30324, 30325, 30326, 30327, 30330, 
    30331, 30333, 30334, 30336, 30337, 
    30345, 30348, 30350, 30351, 30352, 
    30353, 30383, 30405, 30408, 30659, 
    30665, 30696, 30697
  ) 
  AND q_discussion.object_type = "P" 
GROUP BY 
  q_discussion.object_id

Query time 0.00128

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "460.81"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "q_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": 64,
            "rows_produced_per_join": 64,
            "filtered": "100.00",
            "index_condition": "((`portal`.`q_discussion`.`object_id` in (30281,30282,30283,30284,30285,30286,30287,30288,30289,30290,30291,30292,30293,30294,30295,30296,30297,30298,30299,30300,30301,30302,30303,30304,30305,30306,30307,30309,30310,30311,30312,30313,30314,30315,30316,30317,30318,30320,30321,30322,30323,30324,30325,30326,30327,30330,30331,30333,30334,30336,30337,30345,30348,30350,30351,30352,30353,30383,30405,30408,30659,30665,30696,30697)) and (`portal`.`q_discussion`.`object_type` = 'P'))",
            "cost_info": {
              "read_cost": "140.81",
              "eval_cost": "12.80",
              "prefix_cost": "153.61",
              "data_read_per_join": "1024"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type",
              "type"
            ]
          }
        },
        {
          "table": {
            "table_name": "q_discussion_posts",
            "access_type": "ref",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_discussion.thread_id"
            ],
            "rows_examined_per_scan": 2,
            "rows_produced_per_join": 128,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "128.00",
              "eval_cost": "25.60",
              "prefix_cost": "307.21",
              "data_read_per_join": "56K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "<if>(is_not_null_compl(q_discussion_posts), (`portal`.`q_discussion_posts`.`status` = 'A'), true)"
          }
        },
        {
          "table": {
            "table_name": "q_discussion_rating",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "thread_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "post_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_discussion_posts.post_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 128,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "128.00",
              "eval_cost": "25.60",
              "prefix_cost": "460.81",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "rating_value",
              "post_id",
              "thread_id"
            ],
            "attached_condition": "<if>(is_not_null_compl(q_discussion_rating), ((`portal`.`q_discussion_rating`.`thread_id` = `portal`.`q_discussion`.`thread_id`) and (`portal`.`q_discussion_rating`.`rating_value` <> 0)), true)"
          }
        }
      ]
    }
  }
}