matching values

[amar3d]

Hi, i basically have a site where users can only register if they live in a valid post-code area. I have the basic HTML form for inputting the postcode....but what type of query would i need to check there postcode is valid....i have a table postcodes..which has all my post codes listed, and its from this it must match, if anyone can help it would be much appriciated, thanks in advance,
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[Shrike]

A stab in the dark (I take it this is MySQL):

$postcode = validateYourInputs($_POST['postcode']);
$q = "
  SELECT postcode
  FROM postcodes
  WHERE postcode = '$postcode'
";
$r = mysql_query($q);
if(mysql_num_rows($r) == 0)
{
  throw_error("Invalid postcode");
}