SELECT 
  prod.amount 
FROM 
  cscart_products AS prod 
WHERE 
  prod.product_id = 51

Query time 0.00100

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "29.30"
    },
    "table": {
      "table_name": "prod",
      "access_type": "ALL",
      "rows_examined_per_scan": 248,
      "rows_produced_per_join": 24,
      "filtered": "10.00",
      "cost_info": {
        "read_cost": "26.82",
        "eval_cost": "2.48",
        "prefix_cost": "29.30",
        "data_read_per_join": "109K"
      },
      "used_columns": [
        "product_id",
        "amount"
      ],
      "attached_condition": "(`mobikul_delivery_boy_livedemo`.`prod`.`product_id` = 51)"
    }
  }
}