SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 266 
WHERE 
  cscart_products_categories.product_id IN (
    339484, 339755, 430807, 431068, 339697, 
    431359, 430875, 431041, 430825, 430868, 
    431085, 431156, 339681, 339828, 430925, 
    431053, 431164, 381705, 430819, 430820, 
    430901, 431013, 431049, 339596, 430654, 
    430658, 431144, 431148, 430691, 430989, 
    430746, 430808, 430812, 430834, 430629, 
    430680, 431136, 339774, 339765, 430843, 
    339728, 339836, 339843, 431110, 339725, 
    339734, 339816, 431080, 339655, 339839, 
    339599, 431118, 431161, 339466, 430673, 
    430890, 339845, 430789, 430859, 430906, 
    430922, 339582, 339723, 431082, 431126, 
    430657, 430678, 339702, 430737, 430822, 
    430860, 431111, 339674, 430689, 431044, 
    339754, 381704, 430795, 430832, 430892, 
    430914, 430921, 430635, 339802, 339821, 
    430663, 430838, 430854, 431174, 339486, 
    430650, 430959, 431456, 430815, 339727, 
    381697, 431169, 430672, 430695, 430950
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00216

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "281.15"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "link_type",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 100,
            "rows_produced_per_join": 100,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "21.15",
              "eval_cost": "20.00",
              "prefix_cost": "41.15",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (339484,339755,430807,431068,339697,431359,430875,431041,430825,430868,431085,431156,339681,339828,430925,431053,431164,381705,430819,430820,430901,431013,431049,339596,430654,430658,431144,431148,430691,430989,430746,430808,430812,430834,430629,430680,431136,339774,339765,430843,339728,339836,339843,431110,339725,339734,339816,431080,339655,339839,339599,431118,431161,339466,430673,430890,339845,430789,430859,430906,430922,339582,339723,431082,431126,430657,430678,339702,430737,430822,430860,431111,339674,430689,431044,339754,381704,430795,430832,430892,430914,430921,430635,339802,339821,430663,430838,430854,431174,339486,430650,430959,431456,430815,339727,381697,431169,430672,430695,430950))"
          }
        },
        {
          "table": {
            "table_name": "product_position_source",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id",
              "product_id"
            ],
            "key_length": "6",
            "ref": [
              "const",
              "webmarco.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 100,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "100.00",
              "eval_cost": "20.00",
              "prefix_cost": "161.15",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "webmarco.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "100.00",
              "eval_cost": "1.00",
              "prefix_cost": "281.15",
              "data_read_per_join": "29K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`webmarco`.`cscart_categories`.`storefront_id` in (0,1)) and ((`webmarco`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`webmarco`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`webmarco`.`cscart_categories`.`usergroup_ids`)) and (`webmarco`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}