Checking if record exists before insert

[MeSoVarchar]

Hi every1. I have just build a user system but cant figure out how to check if say a unique username/password exists before accepting data from the form. Any ideas?

[MeSoVarchar]

okey, here is my snippet:

<?
db con
$UserName = $_POST['UserName'];
$Password = $_POST['Password'];

/* DB CONNECTION CODE HERE */

$sql = mysql_query("SELECT * FROM Clients WHERE username='$username'");
$result = mysql_num_rows($sql);

if($result !=="0"){
echo "The username you have chosen already exists!";
exit;
} else {

$query = "INSERT INTO Clients (id, FirstName, LastName, Email, Tel, Address, City, PostalCode, Country, UserName, Password ) VALUES ('$id', '$FirstName', '$LastName', '$Email', '$Tel', '$Address', '$City', '$PostalCode', '$Country', '$UserName', '$Password')";

mysql_query($query) or die('mysql error.');

echo "Thank you";
echo "&nbsp;";
}
?>

The damn code still wont work! Says ends at exit even when i have a unique username!

[bokeh]

Password should not need to be unique, only the username. Make the username column type UNIQUE. Then do the INSERT (no prior tests) and then check for a duplicate key error.$result = mysql_query($insert_query);
if(($result !== true) and (mysql_errno() == 1062)
{
# username already in use
}
elseif($result !== true)
{
# query failed for another reason
}
else
{
# INSERT worked ok
}

[aussie girl]

try it without the double quotes around the zero

if($result !== 0){
echo "The username you have chosen already exists!";
exit;