SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    8265, 8270, 8288, 8322, 8350, 8267, 8336, 
    8261, 8186, 8480, 8482, 8411, 8486, 
    8412, 8487, 8489, 8519, 8553, 8559, 
    8568
  )

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "4.36"
    },
    "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": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.36",
        "eval_cost": "2.00",
        "prefix_cost": "4.36",
        "data_read_per_join": "51K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (8265,8270,8288,8322,8350,8267,8336,8261,8186,8480,8482,8411,8486,8412,8487,8489,8519,8553,8559,8568))"
    }
  }
}