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 = 2837 
WHERE 
  cscart_products_categories.product_id IN (
    82071, 82118, 82073, 82038, 149042, 
    82061, 81948, 82009, 82101, 81647, 
    82133, 82103, 81737, 81655, 82104, 
    81704, 81826, 81863, 81741, 81860, 
    81702, 82072, 81634, 81657, 366904, 
    389637, 81739, 81625, 82115, 81776, 
    82074, 81611, 81862, 81627, 366903, 
    82114, 82069, 81773, 81636, 152085, 
    368409, 366900, 366968, 372041, 391071, 
    81624, 82099, 82052, 82096, 391278, 
    359756, 390761, 424699, 430332, 81747, 
    391070, 82116, 82095, 435209, 435210, 
    430344, 430333, 430573, 430346, 430347, 
    435211, 430329
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00269

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "264.35"
    },
    "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": 94,
            "rows_produced_per_join": 94,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "19.95",
              "eval_cost": "18.80",
              "prefix_cost": "38.75",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (82071,82118,82073,82038,149042,82061,81948,82009,82101,81647,82133,82103,81737,81655,82104,81704,81826,81863,81741,81860,81702,82072,81634,81657,366904,389637,81739,81625,82115,81776,82074,81611,81862,81627,366903,82114,82069,81773,81636,152085,368409,366900,366968,372041,391071,81624,82099,82052,82096,391278,359756,390761,424699,430332,81747,391070,82116,82095,435209,435210,430344,430333,430573,430346,430347,435211,430329))"
          }
        },
        {
          "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": 94,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "94.00",
              "eval_cost": "18.80",
              "prefix_cost": "151.55",
              "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": 4,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "94.00",
              "eval_cost": "0.94",
              "prefix_cost": "264.35",
              "data_read_per_join": "27K"
            },
            "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')))"
          }
        }
      ]
    }
  }
}