SELECT 
  p.product_id, 
  ifnull(
    count(dp.post_id), 
    0
  ) as discussion_amount_posts 
FROM 
  q_discussion 
  INNER JOIN q_products as p ON (
    q_discussion.object_id = p.product_id
  ) 
  INNER JOIN q_discussion_posts as dp ON (
    q_discussion.thread_id = dp.thread_id 
    AND q_discussion.object_type = 'P'
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    1737, 1747, 1748, 1749, 1745, 1751, 1752, 
    1753, 1754, 1931, 2167, 2169, 2170, 
    2171, 2172, 2173, 2174, 2175, 2176, 
    1941, 2178, 2179, 2180, 2181, 2182, 
    2183, 2184, 2185, 2186, 1951, 2187, 
    2189, 2190, 1955, 2191, 2192, 2193, 
    2194, 2195, 2196, 2197, 2198, 2199, 
    2200, 2201, 2203, 2204, 2205, 1970, 
    2206, 2208, 2209, 2210, 2211, 2212, 
    2213, 2214, 2215, 2216, 2217, 2218, 
    2219, 2220, 1985, 2223, 2224, 2225, 
    2226, 2227, 2228, 2229, 2230, 2231, 
    2232, 2233, 2234, 2235, 2236, 2000, 
    2238, 2239, 2240, 1388, 8679, 8680
  ) 
GROUP BY 
  p.product_id

Query time 0.00081

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "21.61"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "0.29"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "dp",
            "access_type": "ALL",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "rows_examined_per_scan": 57,
            "rows_produced_per_join": 5,
            "filtered": "10.00",
            "cost_info": {
              "read_cost": "13.01",
              "eval_cost": "1.14",
              "prefix_cost": "14.15",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "(`portal`.`dp`.`status` = 'A')"
          }
        },
        {
          "table": {
            "table_name": "q_discussion",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "object_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.dp.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "5.70",
              "eval_cost": "0.06",
              "prefix_cost": "20.99",
              "data_read_per_join": "4"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type"
            ],
            "attached_condition": "((`portal`.`q_discussion`.`object_id` in (1737,1747,1748,1749,1745,1751,1752,1753,1754,1931,2167,2169,2170,2171,2172,2173,2174,2175,2176,1941,2178,2179,2180,2181,2182,2183,2184,2185,2186,1951,2187,2189,2190,1955,2191,2192,2193,2194,2195,2196,2197,2198,2199,2200,2201,2203,2204,2205,1970,2206,2208,2209,2210,2211,2212,2213,2214,2215,2216,2217,2218,2219,2220,1985,2223,2224,2225,2226,2227,2228,2229,2230,2231,2232,2233,2234,2235,2236,2000,2238,2239,2240,1388,8679,8680)) and (`portal`.`q_discussion`.`object_type` = 'P'))"
          }
        },
        {
          "table": {
            "table_name": "p",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "ref": [
              "portal.q_discussion.object_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "0.29",
              "eval_cost": "0.06",
              "prefix_cost": "21.33",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id"
            ]
          }
        }
      ]
    }
  }
}