SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    40162, 40150, 21174, 20833, 20978, 21367, 
    19539, 21181, 19535, 20814, 19454, 
    19447, 19449, 19549, 20997
  )

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.85"
    },
    "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": 31,
      "rows_produced_per_join": 31,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "3.75",
        "eval_cost": "3.10",
        "prefix_cost": "6.85",
        "data_read_per_join": "80K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (40162,40150,21174,20833,20978,21367,19539,21181,19535,20814,19454,19447,19449,19549,20997))"
    }
  }
}

Result