bindValue is not working - php

Question

Using PDO with MariaDB server. I am having trouble understanding why this code does not work. Whenever I have :value for the values it gives me an error " Invalid parameter number: parameter was not defined"
$sql = "INSERT INTO table (USER, DOMAIN,FLG) VALUES (:username,:domain,:flag)";
$stmt = $dbh->prepare($sql);
$stmt->bindValue(':username', $username);
$stmt->bindValue(':domain', $domain);
$stmt->bindValue(':flag', $flag);
$stmt->execute();
But then the code below does work.
$sql = "INSERT INTO table (USER, DOMAIN,FLG) VALUES (?,?,?)";
$stmt = $dbh->prepare($sql);
$stmt->bindValue(1, $username);
$stmt->bindValue(2, $domain);
$stmt->bindValue(3, $flag);
$stmt->execute();
Below is the rest of the section for this code.
if(isset($_POST['addEditor'])){
$username = $_POST['formUsername'];
$domain = $_POST['formDomain'];
$flag = $_POST['formflg'];
$sql = "INSERT INTO table (USER, DOMAIN,FLG) VALUES (:username,:domain,:flag)";
$stmt = $dbh->prepare($sql);
$stmt->bindValue(':username', $username);
$stmt->bindValue(':domain', $domain);
$stmt->bindValue(':flag', $flag);
$stmt->execute();
try{
$stmt->execute();
}
catch (Exception $e) {
die ('ERROR: ' . $e->getMessage());
}

Answer 1

That code worked for me have read something about PDO here
$dbh = new PDO("mysql:host=$dbhost;dbname=$dbname",$dbuser,$dbpass);
$username='a';
$domain ='b';
$flag ='c';
$sql = "INSERT INTO `table` (`USER`, `DOMAIN`, `FLG`) VALUES (:username,:domain,:flag)";
$stmt = $dbh->prepare($sql);
$stmt->execute(
array(':username'=> $username,
':domain'=> $domain,
':flag'=> $flag)
);

Answer 2

I am having trouble understanding why this code does not work.
No wonder, as you're using wrong way to understand.
Get rid of all try and catch operators in your code, run it again and then read the full error message, that will make you understand which code does not work.

Answer 3

if($_POST)
{
$role ="student";
try{
$stmt = $db_con->prepare("INSERT INTO userinfo (role)
VALUES(:qrole)");
$stmt->bindParam(":qrole", $role);
if($stmt->execute())
{
echo "Successfully Added";
}
else{
echo "Query Problem";
}
}
catch(PDOException $e){
echo $e->getMessage();
}
}
try this , if some errors occurred it will post it using catch