mysql - After login in to the profile how to insert some other columns data into same database in php -

i have signup form. once create form data inserted registered table once after login form need fill details , insert same columns comparing mail ids. when i'm trying insert data showing not inserted database.

dashboard.php:

 <form method="post" action="personalinfo.php" id="myform">     <input type='hidden' value="<?php echo $_get['email'];?>" name='email'>             <div>           <label for="first-name">first name<span class="mandatory">*</span></label>           <input id="first-name"  type="text" name="first-name" value="" />         </div>          <button type="submit" id = "submit" class="btn btn-success btn-block"><span class="glyphicon glyphicon-off"></span> save</button> 

personalinfo.php:

 <?php  $connection = mysql_connect("localhost", "root", "") or die(mysql_error());  $db = mysql_select_db("accountant", $connection);  $email=$_post['email'];  $firstname = $_post['first-name'];  $query = mysql_query("insert registered (first-name)  values ('$firstname') select email registered email!='$email'  "); mysql_query("$query") or die("error:".mysql_error()); if($query) {     echo "successfully registered";          } else{     echo "registration has not been completed.please try again"; } ?> 

if use mysql_error showing query empty.

this complete set of answer comments.

<?php   $connection = mysql_connect("localhost", "root", "") or die(mysql_error()); $db = mysql_select_db("accountant", $connection);  $email=$_post['email']; $firstname = $_post['first_name'];  // check if email registered $res = mysql_query("select email registered email='$email");   if(!$res || mysql_num_rows($res)<1){ // if not add record   $query = mysql_query("insert registered (first_name, email) values ('$firstname', '$email')") or die("error:".mysql_error()); }else{ // if email present update record $query = mysql_query("update registered set first_name='$firstname'" email= '$email') or die("error:".mysql_error()); }  if($query)  {      echo "successfully registered";          }  else{     echo "registration has not been completed.please try again";  } }