[PHP] Gibt kein Echo aus?

<?php 
	require 'config.php';
	require 'include/sqlcon.php';

	/*if($pin > 0) {
		if($_GET["key"] != round(date("H") * $pin, 4)) {
			die("Falsche PIN!");
		}
	}*/

	if(!empty($_GET["action"])) {
		#if($_SERVER['HTTP_USER_AGENT'] != 'AutoHotkey' && AHK_ONLY) die("Keine Berechtigung!");
		$table = $_GET['table'];

		switch($_GET["action"]) {
			case "read": {
				if(!empty($_GET['a']) && !empty($_GET['b']) && !empty($_GET['c']))
				{	
					$stmt = getDB()->prepare("SELECT `:clm` FROM `:table` WHERE `:row` = ':rw'");
					$stmt->execute(array(
						'clm' => $_GET['a'],
						'table' => $table,
						'row' => $_GET['b'],
						'rw' => $_GET['c']
					));		

					if($stmt->rowCount()) {
						$obj = $stmt->fetch(PDO::FETCH_OBJ);

						if(!$obj) {
							echo "0";
						} else {
							echo $obj[0];
						}
					} else {
						echo "-1";
					}
				}
				break;
			}
			case "write": {
				if(!empty($_GET['a']) && !empty($_GET['b']) && !empty($_GET['c']) && !empty($_GET['d']))
				{	
					$stmt = getDB()->prepare("UPDATE `:table` SET `:clm` = `:val` WHERE `:cl` = ':rw'");
					$stmt->execute(array(
						'table' => $table,
						'clm' => $_GET['a'],
						'val' => $_GET['b'],
						'cl' => $_GET['c'],
						'rw' => $_GET['d']
					));		

					if(!$stmt) {
						echo "0";
					} else {
						echo "1";
					}
				}
				break;
			}
			case "compare": {
				if(!empty($_GET['a']) && !empty($_GET['b']) && !empty($_GET['c']) && !empty($_GET['d']))
				{	
					$stmt = getDB()->prepare("SELECT `:clm` FROM `:table` WHERE `:row` = ':val'");
					$stmt->execute(array(
						'clm' => $_GET['a'],
						'table' => $table,
						'row' => $_GET['b'],
						'val' => $_GET['c']
					));		

					if($stmt->rowCount()) {
						$res = $stmt->fetch(PDO::FETCH_OBJ);
						if($res->$_GET['a'] == $_GET['d']) {
							echo "1";
						} else {
							echo "0";
						}
					} else {
						echo "-1";
					}
				}
				break;
			}
			case "row_exist": {
				echo "row exist.";
				if(!empty($_GET['a']) && !empty($_GET['b']))
				{	
					$stmt = getDB()->prepare("SELECT * FROM `:table` WHERE `:row` = ':val'");
					$stmt->execute(array(
						'table' => $_GET['table'],
						'row' => $_GET['a'],
						'val' => $_GET['b']
					));				

					if($stmt->rowCount()) {
						echo "1";
					} else {
						echo "0";
					}
				}
			}
		}
	}
?>

case "row_exist": {
				echo "row exist.";
				if(!empty($_GET['a']) && !empty($_GET['b']))
				{	
					$stmt = getDB()->prepare("SELECT * FROM `:table` WHERE `:row` = ':val'");
					$stmt->execute(array(
						'table' => $table,
						'row' => $_GET['a'],
						'val' => $_GET['b']
					));				

					if($stmt->rowCount()) {
						echo "1";
					} else {
						echo "0";
					}
				}
			}