SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    40162, 40150, 19455, 21174, 20816, 21166, 
    19550, 20824, 20833, 21338, 20818, 
    20978, 19448, 21367, 19539, 19560, 
    21165, 21181, 19535, 19537, 20821, 
    19500, 19453, 20814, 19538, 21161, 
    19454, 19447, 19449, 19549, 21167, 
    20997, 20822, 21365, 19450, 19536
  )

Query time 0.00049

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "11.06"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 52,
      "rows_produced_per_join": 52,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "5.86",
        "eval_cost": "5.20",
        "prefix_cost": "11.06",
        "data_read_per_join": "134K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (40162,40150,19455,21174,20816,21166,19550,20824,20833,21338,20818,20978,19448,21367,19539,19560,21165,21181,19535,19537,20821,19500,19453,20814,19538,21161,19454,19447,19449,19549,21167,20997,20822,21365,19450,19536))"
    }
  }
}

Result