Help!!

[阿豐]

$result=0;
$query="select * from users where user_id='$user_id'";
$result=mysql_query($query,$link);
if(mysql_fetch_row($result)) $result=1;
else $result=0;

I use the function of "mysql_fetch_row()" in register2.php
and it's output is the follow list:

Warning: Supplied argument is not a valid MySQL result resource in 
/home/shin/public_html/register2.php on line 27