SELECT 
  page_id 
FROM 
  cscart_pages 
WHERE 
  page_type = 'B' 
  AND parent_id = 0 
ORDER BY 
  page_id DESC

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "3.60"
    },
    "ordering_operation": {
      "using_filesort": true,
      "table": {
        "table_name": "cscart_pages",
        "access_type": "ref",
        "possible_keys": [
          "parent_id"
        ],
        "key": "parent_id",
        "used_key_parts": [
          "parent_id"
        ],
        "key_length": "3",
        "ref": [
          "const"
        ],
        "rows_examined_per_scan": 22,
        "rows_produced_per_join": 2,
        "filtered": "10.00",
        "cost_info": {
          "read_cost": "1.40",
          "eval_cost": "0.22",
          "prefix_cost": "3.60",
          "data_read_per_join": "5K"
        },
        "used_columns": [
          "page_id",
          "parent_id",
          "page_type"
        ],
        "attached_condition": "(`dbggbern`.`cscart_pages`.`page_type` = 'B')"
      }
    }
  }
}