SELECT 
  id, 
  winner_user_id 
FROM 
  cscart_auction 
WHERE 
  `product_id` = 1038 
  AND `status` = 'A' 
  AND `buy` = 'no' 
  AND `auto_win` = 1

Query time 0.00055

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}