Php function question

function getAll($what, $tableName, $where=null)
{
	global $db_conn;
	if($where == null)
	{
		$query = mysqli_query($db_conn, "SELECT  $what  FROM `$tableName`");
		return $query;
	}
	else
	{
		$query = mysqli_query($db_conn, "SELECT  $what  FROM `$tableName` WHERE  $where");
		return $query;
	}
	mysqli_close();
}

function getSingle($what, $tableName, $where=null)
{
	$result = getAll($what, $tableName, $where);
	$row = mysqli_fetch_array($result);
	return $row["$what"];
	mysqli_close();
}

function getCount($tableName, $where=null)
{
	$result = getAll('*', $tableName, $where);
	return mysqli_num_rows($result);
	mysqli_close();
}

$error =false;


if(isset($_POST['login']))
{
	$status = 'admin';
	$email_user='';
	$own_email=$_POST['email_user'];
	$adm_email=$_POST['email_user'];
	$Password = $_POST['Password'];
	$staf_username = $_POST['email_user'];
	$stu_username = $_POST['email_user'];
	$own_email = filter_var($email_user, FILTER_VALIDATE_EMAIL);
	$Password = hash('sha256','password');
	$Password = strip_tags(addslashes($Password));

	$count = getCount('owners_db', "own_email ='$own_email'");
	$count1 = getCount('staff_db', "staf_username ='$staf_username' ");
	$count2 = getCount('student_db', "stu_username ='$stu_username' ");
	// this is for the admin
	$count3 = getCount('admin_db', "adm_email ='$adm_email'");
	
	if ($count != 0) {
		$own_id = getSingle('own_id', 'owners_db', "own_email = '$own_email' AND Password = '$Password'");
		return;
	}
	elseif($count == 0){
		$error=true;
		$errormsg1= '<div id="success" class="alert red">Invalid email or password!</div>';
		return;
	}
	elseif($count == 1){

		$_SESSION['own_email'] = $own_email;
		$update = update('owners_db', "last_login=now()", "own_email='$own_email'");

		header('location: owners_dashboard');
		return;
	}// count

this is the error am getting please i need help 

<pre>Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\altech-school\server\dbase\database.php on line 74

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\altech-school\server\dbase\database.php on line 74

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\altech-school\server\dbase\database.php on line 74

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\altech-school\server\dbase\database.php on line 74

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\altech-school\server\dbase\database.php on line 74

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\altech-school\server\dbase\database.php on line 74