$result = mysql_query("SELECT product.pcode,pname,brand,price,oldbal,receipt,total,current,sales.date FROM product,sales WHERE sales.date='$date' AND product.pcode=sales.pcode");

SELECT product.pcode,pname,brand,price,oldbal,receipt,total,current,sales.date
FROM product LEFT JOIN sales
ON product.pcode=sales.pcode
WHERE sales.date=$date

SELECT product.pcode,pname,brand,price,oldbal,receipt,total,current,sales.date FROM product LEFT JOIN sales ON product.pcode = sales.pcode WHERE sales.date='$date';