You should look at the documentation. But If you dont find anything, you can add another catch :

<?phptry {  $stmt = $db->prepare("INSERT INTO tbl_user (id, name, password, question, answer)    VALUES (NULL, :name, :password, :question, :answer)");  $stmt->bindValue(":name", $_POST['name']);  $stmt->bindValue(":password", $_POST['password']);  $stmt->bindValue(":question", $_POST['question']);  $stmt->bindValue(":answer", $_POST['answer']);  $stmt->execute();  echo "Successfully added the new user " . $_POST['name'];} catch (PDOException $e) {  echo "DataBase Error: The user could not be added.<br>".$e->getMessage();} catch (Exception $e) {  echo "General Error: The user could not be added.<br>".$e->getMessage();}?>

This must work because all exceptions of PHP plugins herits from the Exception native PHP class. (Since 5.0 if my memory is well).

PDO Exception Questions - How to Catch Them

As a rule -

DO NOT catch them.

For example, your code here should be written this way

$stmt = $db->prepare("INSERT INTO tbl_user (id, name, password, question, answer) VALUES (NULL, :name, :password, :question, :answer)");$stmt->bindValue(":name", $_POST['name']);$stmt->bindValue(":password", $_POST['password']);$stmt->bindValue(":question", $_POST['question']);$stmt->bindValue(":answer", $_POST['answer']);$stmt->execute();echo "Successfully added the new user " . $_POST['name'];

without any try or catch calls. Because you have no particular scenario for handling an exception here (a simple echo is scarcely counts as a handling scenario).

Instead, let it bubble up to the application-wide error handler (don't be scared by the term, PHP already has a built-in one).

However, I'm having issues catching the errors how I'd like (errors like "Duplicate Entry", "Null Value" etc in MySQL).

Only in case if you have a certain scenario, you have to use try-catch operator, but you have to always check, whether the error you've got is one you expected. Otherwise an exception have to be re-thrown:

try {    $pdo->prepare("INSERT INTO users VALUES (NULL,?,?,?,?)")->execute($data);} catch (PDOException $e) {    if ($e->getCode() == 1062) {        // Take some action if there is a key constraint violation, i.e. duplicate name    } else {        throw $e;    }}

and of course (as it turned out to be the vere problem for this question), you have to set up PDO in exception mode, either in a constructor parameter of simply by adding the code

$db->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

right after connect.

JUST THROW ERROR PROPERLY WHEN MADE NEW PDO CONNECTION

       try{  try{            $this->pdo = new \PDO($this->dsn,$this->options);            $this->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES,false);            //Display PDO Errors            $this->pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);        }catch (\PDOException $e) {            throw new CustomException ($e->getMessage());        }    }catch (CustomException $e)    {        $e->render();    }