error in sql statement

[nazish zehra]

I am making a from in php and inserting values in members table.Structure of members table is:
id varchar(30) not null primary key
username varchar(15)
password varchar(15)

when i insert values in table using $_POST[] it gives error
Error:Duplicate entry 'john' for key 'PRIMARY' whereas there is no entry in my table as john.Code is:

<?php
$con = mysql_connect("localhost","root","");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }
mysql_select_db("seed_bank", $con);
 
$sql = "insert into members(id,username,password) 
values('$_POST[emailid]','$_POST[firstname]','$_POST[password]')";
print $sql;
$result=mysql_query($sql);
$count=mysql_num_rows($result);
if($count==1)
{
echo "Registration SUCCCESSFUL";
}
 
if(!mysql_query($sql,$con))
{
die('Error:'.mysql_error());
}
 
else {echo"Registration succcessful";}
mysql_close($con);
?>
 

It gives the error but at the same time also inserts values in the table.why it is giving error even when inserting values in the table?

[Rabbit]

It's because you run your query twice. Once on line 12 and again on line 19.