SELECT 
  p.product_id, 
  ifnull(
    count(dp.post_id), 
    0
  ) as discussion_amount_posts 
FROM 
  cscart_discussion 
  INNER JOIN cscart_products as p ON (
    cscart_discussion.object_id = p.product_id
  ) 
  INNER JOIN cscart_discussion_posts as dp ON (
    cscart_discussion.thread_id = dp.thread_id 
    AND cscart_discussion.object_type = 'P'
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    359808, 
    309567, 
    309571, 
    309585, 
    309586, 
    309587, 
    309588, 
    309590, 
    359478, 
    359805, 
    435519, 
    359744, 
    359746, 
    359752, 
    359753, 
    359758, 
    359772, 
    372040, 
    381634, 
    387082, 
    395983, 
    395984, 
    395985, 
    395986, 
    395987, 
    395988, 
    395989, 
    395990, 
    395991, 
    395992, 
    395993, 
    395994, 
    395995, 
    395996, 
    395997, 
    395998, 
    395999, 
    396000, 
    396001, 
    396002, 
    396003, 
    396004, 
    396005, 
    396006, 
    396007, 
    396008, 
    396009, 
    396010, 
    396011, 
    396012, 
    396013, 
    396014, 
    396015, 
    396016, 
    396017, 
    396018, 
    396019, 
    396020, 
    396021, 
    396022, 
    396023, 
    396024, 
    396025, 
    396027, 
    396028, 
    396029, 
    396030, 
    396031, 
    396032, 
    396033, 
    396034, 
    396035, 
    396037, 
    396038, 
    396039, 
    396040, 
    396041, 
    396042, 
    396044, 
    396045, 
    396046, 
    396047, 
    396048, 
    396049, 
    396050, 
    396052, 
    396053, 
    396054, 
    396055, 
    396056, 
    396057, 
    396058, 
    396059, 
    396060, 
    396061, 
    396062, 
    396063, 
    396064, 
    396065, 
    396066, 
    396067, 
    396074, 
    396075, 
    396076, 
    396077, 
    396078, 
    396079, 
    396080, 
    396081, 
    396082, 
    396083, 
    396084, 
    396085, 
    414316, 
    414317, 
    414318, 
    414319, 
    414320, 
    414321, 
    414323, 
    414324, 
    414325, 
    414326, 
    414327, 
    414328, 
    414329, 
    414330, 
    414331, 
    414332, 
    414333, 
    414334, 
    414335, 
    414336, 
    414337, 
    414338, 
    414339, 
    414340, 
    414341, 
    414342, 
    414343, 
    414344, 
    414345, 
    414346, 
    414347, 
    414348, 
    414349, 
    414350, 
    414351, 
    414352, 
    414353, 
    414354, 
    414355, 
    414356, 
    414357, 
    414358, 
    414359, 
    414360, 
    414361, 
    414362, 
    414363, 
    414364, 
    414365, 
    414366, 
    414393, 
    414394, 
    414395, 
    414396, 
    414397, 
    414398, 
    414399, 
    414401, 
    414402, 
    414403, 
    414404, 
    414405, 
    414406, 
    414407, 
    414408, 
    414409, 
    414410, 
    414411, 
    414412, 
    414413, 
    414415, 
    414416, 
    414417, 
    414418, 
    414419, 
    414420, 
    414421, 
    414422, 
    414423, 
    414424, 
    414425, 
    414426, 
    414427, 
    414428, 
    414429, 
    414430, 
    414431, 
    414432, 
    414433, 
    414434, 
    414435, 
    414436, 
    414437, 
    414438, 
    414439, 
    414440, 
    414441, 
    414443, 
    414444, 
    414445, 
    414446, 
    414447, 
    414448, 
    414449, 
    414450, 
    414451, 
    414452, 
    414453, 
    414459, 
    414460, 
    414461, 
    414462, 
    414463, 
    414464, 
    414465, 
    414468, 
    414470, 
    414471, 
    414472, 
    414473, 
    414474, 
    414475, 
    414476, 
    414488, 
    414491, 
    414492, 
    414493, 
    414494, 
    414495, 
    414496, 
    414507, 
    414508, 
    414509, 
    414510, 
    414511, 
    414512, 
    414525, 
    414527, 
    414528, 
    414529, 
    414530, 
    414531, 
    414534, 
    414535, 
    414536, 
    414537, 
    414538, 
    414541, 
    414542, 
    414543, 
    414544, 
    414545, 
    431506, 
    431507, 
    431508, 
    431509, 
    431510, 
    431511, 
    431512, 
    431513, 
    431514, 
    431515, 
    431516, 
    431517, 
    431518, 
    431519, 
    431520, 
    431521, 
    431522, 
    431523, 
    431524, 
    431525, 
    431526, 
    431527, 
    431528, 
    431529, 
    431530, 
    431531, 
    431532, 
    431533, 
    431534, 
    431535, 
    431536, 
    431537, 
    431542, 
    431543, 
    431544, 
    431545, 
    431546, 
    431547, 
    431548, 
    431549, 
    431550, 
    431551, 
    431677, 
    431678, 
    431679, 
    431680, 
    431681, 
    431682, 
    431683, 
    431684, 
    431685, 
    431686, 
    431561, 
    431562, 
    431563, 
    431564, 
    431565, 
    431566, 
    431567, 
    431568, 
    431569, 
    431587, 
    431588, 
    431589, 
    431590, 
    431591, 
    431592, 
    431593, 
    431594, 
    431595, 
    431596, 
    431597, 
    431598, 
    431599, 
    431600, 
    431601, 
    431602, 
    431603, 
    431604, 
    431579, 
    431580, 
    431581, 
    431582, 
    431583, 
    431584, 
    431585, 
    431586, 
    431605, 
    431606, 
    431607, 
    431608, 
    431609, 
    431610, 
    431611, 
    431612, 
    431613, 
    431614, 
    431615, 
    431616, 
    431617, 
    431618, 
    431619, 
    431620, 
    431621, 
    431622, 
    431623, 
    431624, 
    431625, 
    431626, 
    431627, 
    431628, 
    431629, 
    431630, 
    431631, 
    431632, 
    431633, 
    431634, 
    431635, 
    431636, 
    431637, 
    431638, 
    431639, 
    431640, 
    431641, 
    431642, 
    431643, 
    431644, 
    431645, 
    431646, 
    431647, 
    431648, 
    431649, 
    431650, 
    431651, 
    431652, 
    431653, 
    431654, 
    431655, 
    431656, 
    431657, 
    431658, 
    431659, 
    431660, 
    431661, 
    431662, 
    431663, 
    431664, 
    431665, 
    431666, 
    431667, 
    431668, 
    431669, 
    431670, 
    431671, 
    431734, 
    431735, 
    431736, 
    431737, 
    431738, 
    431739, 
    431740, 
    431741, 
    431742, 
    431767, 
    431768, 
    431769, 
    431770, 
    431771, 
    431772, 
    431773, 
    431774, 
    431775
  ) 
GROUP BY 
  p.product_id

Query time 0.00301

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "7.29"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "0.10"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "dp",
            "access_type": "index",
            "possible_keys": [
              "thread_id",
              "thread_id_2"
            ],
            "key": "thread_id_2",
            "used_key_parts": [
              "thread_id",
              "status"
            ],
            "key_length": "6",
            "rows_examined_per_scan": 19,
            "rows_produced_per_join": 1,
            "filtered": "10.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "4.42",
              "eval_cost": "0.38",
              "prefix_cost": "4.80",
              "data_read_per_join": "851"
            },
            "used_columns": [
              "post_id",
              "thread_id",
              "status"
            ],
            "attached_condition": "(`webmarco`.`dp`.`status` = 'A')"
          }
        },
        {
          "table": {
            "table_name": "cscart_discussion",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "object_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "thread_id"
            ],
            "key_length": "3",
            "ref": [
              "webmarco.dp.thread_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "1.90",
              "eval_cost": "0.02",
              "prefix_cost": "7.08",
              "data_read_per_join": "2"
            },
            "used_columns": [
              "thread_id",
              "object_id",
              "object_type"
            ],
            "attached_condition": "((`webmarco`.`cscart_discussion`.`object_id` in (359808,309567,309571,309585,309586,309587,309588,309590,359478,359805,435519,359744,359746,359752,359753,359758,359772,372040,381634,387082,395983,395984,395985,395986,395987,395988,395989,395990,395991,395992,395993,395994,395995,395996,395997,395998,395999,396000,396001,396002,396003,396004,396005,396006,396007,396008,396009,396010,396011,396012,396013,396014,396015,396016,396017,396018,396019,396020,396021,396022,396023,396024,396025,396027,396028,396029,396030,396031,396032,396033,396034,396035,396037,396038,396039,396040,396041,396042,396044,396045,396046,396047,396048,396049,396050,396052,396053,396054,396055,396056,396057,396058,396059,396060,396061,396062,396063,396064,396065,396066,396067,396074,396075,396076,396077,396078,396079,396080,396081,396082,396083,396084,396085,414316,414317,414318,414319,414320,414321,414323,414324,414325,414326,414327,414328,414329,414330,414331,414332,414333,414334,414335,414336,414337,414338,414339,414340,414341,414342,414343,414344,414345,414346,414347,414348,414349,414350,414351,414352,414353,414354,414355,414356,414357,414358,414359,414360,414361,414362,414363,414364,414365,414366,414393,414394,414395,414396,414397,414398,414399,414401,414402,414403,414404,414405,414406,414407,414408,414409,414410,414411,414412,414413,414415,414416,414417,414418,414419,414420,414421,414422,414423,414424,414425,414426,414427,414428,414429,414430,414431,414432,414433,414434,414435,414436,414437,414438,414439,414440,414441,414443,414444,414445,414446,414447,414448,414449,414450,414451,414452,414453,414459,414460,414461,414462,414463,414464,414465,414468,414470,414471,414472,414473,414474,414475,414476,414488,414491,414492,414493,414494,414495,414496,414507,414508,414509,414510,414511,414512,414525,414527,414528,414529,414530,414531,414534,414535,414536,414537,414538,414541,414542,414543,414544,414545,431506,431507,431508,431509,431510,431511,431512,431513,431514,431515,431516,431517,431518,431519,431520,431521,431522,431523,431524,431525,431526,431527,431528,431529,431530,431531,431532,431533,431534,431535,431536,431537,431542,431543,431544,431545,431546,431547,431548,431549,431550,431551,431677,431678,431679,431680,431681,431682,431683,431684,431685,431686,431561,431562,431563,431564,431565,431566,431567,431568,431569,431587,431588,431589,431590,431591,431592,431593,431594,431595,431596,431597,431598,431599,431600,431601,431602,431603,431604,431579,431580,431581,431582,431583,431584,431585,431586,431605,431606,431607,431608,431609,431610,431611,431612,431613,431614,431615,431616,431617,431618,431619,431620,431621,431622,431623,431624,431625,431626,431627,431628,431629,431630,431631,431632,431633,431634,431635,431636,431637,431638,431639,431640,431641,431642,431643,431644,431645,431646,431647,431648,431649,431650,431651,431652,431653,431654,431655,431656,431657,431658,431659,431660,431661,431662,431663,431664,431665,431666,431667,431668,431669,431670,431671,431734,431735,431736,431737,431738,431739,431740,431741,431742,431767,431768,431769,431770,431771,431772,431773,431774,431775)) and (`webmarco`.`cscart_discussion`.`object_type` = 'P'))"
          }
        },
        {
          "table": {
            "table_name": "p",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "age_verification",
              "status",
              "idx_parent_product_id",
              "idx_master_product_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "ref": [
              "webmarco.cscart_discussion.object_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "0.10",
              "eval_cost": "0.02",
              "prefix_cost": "7.19",
              "data_read_per_join": "760"
            },
            "used_columns": [
              "product_id"
            ]
          }
        }
      ]
    }
  }
}