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 (
    431456, 339702, 387049, 339593, 430751, 
    431148, 430660, 430825, 431127, 430680, 
    430691, 430820, 431013, 430678, 339849, 
    430875, 430959, 431194, 431035, 431041, 
    431044, 431049, 431109, 339483, 339484, 
    431083, 339820, 430737, 430756, 430989, 
    431080, 431161, 430635, 339734, 381698, 
    381699, 430650, 430922, 430808, 430819, 
    430843, 430629, 430657, 430807, 339596, 
    430868, 430921, 431126, 431144, 430795, 
    430928, 431073, 431082, 430789, 430812, 
    430950, 339725, 430658, 430758, 430901, 
    431110, 339674, 430818, 431156, 339774, 
    339728, 339754, 430673, 430689, 430822, 
    430860, 431114, 339821, 339836, 430684, 
    430664, 430769, 430892, 431043, 431066, 
    431169, 339466, 381705, 430842, 430628, 
    430834, 431064, 339843, 339802, 430859, 
    431459, 430906, 381697, 430768, 430890, 
    430962, 431118, 431250, 430703, 430988
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00333

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 (431456,339702,387049,339593,430751,431148,430660,430825,431127,430680,430691,430820,431013,430678,339849,430875,430959,431194,431035,431041,431044,431049,431109,339483,339484,431083,339820,430737,430756,430989,431080,431161,430635,339734,381698,381699,430650,430922,430808,430819,430843,430629,430657,430807,339596,430868,430921,431126,431144,430795,430928,431073,431082,430789,430812,430950,339725,430658,430758,430901,431110,339674,430818,431156,339774,339728,339754,430673,430689,430822,430860,431114,339821,339836,430684,430664,430769,430892,431043,431066,431169,339466,381705,430842,430628,430834,431064,339843,339802,430859,431459,430906,381697,430768,430890,430962,431118,431250,430703,430988))"
          }
        },
        {
          "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')))"
          }
        }
      ]
    }
  }
}