SELECT 
  user_id, 
  in_auction, 
  location 
FROM 
  cscart_sg_old_product_sell 
WHERE 
  product_id = 17126

Query time 0.00035

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.05"
    },
    "table": {
      "table_name": "cscart_sg_old_product_sell",
      "access_type": "ALL",
      "rows_examined_per_scan": 8,
      "rows_produced_per_join": 1,
      "filtered": "12.50",
      "cost_info": {
        "read_cost": "0.95",
        "eval_cost": "0.10",
        "prefix_cost": "1.05",
        "data_read_per_join": "800"
      },
      "used_columns": [
        "user_id",
        "product_id",
        "location",
        "in_auction"
      ],
      "attached_condition": "(`dev_yourmart_co_bw`.`cscart_sg_old_product_sell`.`product_id` = 17126)"
    }
  }
}