SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    8209, 8277, 8294, 8355, 8382, 8383, 8173, 
    8208, 8431, 8496, 8456, 8466, 8492, 
    8494, 8293, 8338, 8510, 8245, 8439, 
    8511, 8565, 8354
  )

Query time 0.00046

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.23"
    },
    "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": 22,
      "rows_produced_per_join": 22,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "3.03",
        "eval_cost": "2.20",
        "prefix_cost": "5.23",
        "data_read_per_join": "57K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`maniamall_cscart`.`cscart_categories`.`parent_id` in (8209,8277,8294,8355,8382,8383,8173,8208,8431,8496,8456,8466,8492,8494,8293,8338,8510,8245,8439,8511,8565,8354))"
    }
  }
}