Problems with code to change value

[OriginalSunny]

Hi,
My form outputs the quantity and productID correctly on the form but i can't seem to decrease the amount for quantity by the quantity output.

while($row1 = mysql_fetch_array($result1))
{
echo "<td><b>";
echo ''.$row1['quantity'].'';
echo "</b></td>&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp";
echo "<td><b>";
echo ''.$row1['stockID'].'';
[b] $sql = REPLACE INTO Stock (stockAmt) VALUES (" stockAmt - ''.$row1['quantity'].'' ")
WHERE stockID = " ''.$row1['stockID'].'' ";
mysql_query($sql);[/b]
}

The problem is the code in bold. I don't get where i am going wrong as the correct values are ouput but when i use the bit to replace the value, it causes a blank output so there is an error somewhere. If you know what it is please let me know.
Thanks.

[poirot]

Try this one:

[code]$sql = 'REPLACE INTO Stock (stockAmt) VALUES (" stockAmt - ' . $row1['quantity']. ' ") WHERE stockID = "' . $row1['stockID']. ' " ';[/code]

[OriginalSunny]

Tried it, still a blank page.