SELECT 
  * 
FROM 
  tmall_ab__eb_price_tracking_discounts pt_disc 
WHERE 
  1 
  AND pt_disc.storefront_id = 1 
ORDER BY 
  pt_disc.days asc

Query time 0.00853

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.011647987,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "pt_disc.days",
            "table": {
              "table_name": "pt_disc",
              "access_type": "ALL",
              "loops": 1,
              "rows": 1,
              "cost": 0.0110178,
              "filtered": 100,
              "attached_condition": "pt_disc.storefront_id = 1"
            }
          }
        }
      }
    ]
  }
}