要知道为什么会出现空白屏幕，您必须打开error_reporting，请在php代码开头添加以下内容:

to know why you get a blank screen you have to turn on error_reporting, add the following at the start of your php code before anything else:

error_reporting(-1);

还添加一些代码来显示MySQL中可能发生的错误:

Also add some code to show errors that might happen in MySQL:

if(isset($UserID)) {    

$users = $con->prepare("
SELECT DISTINCT
     d.FirstName                
    ,d.LastName                 
    ,d.Picture  
FROM Details  
WHERE d.UserId = ?
");
if (!$users) {
    echo 'MySQL Connect Error in Query: (' . $mysqli->errno . ') ';
}

$binding = $users->bind_param('i', $GetUserId);
if (!$binding) {
    echo 'MySQL Connect Error in Query: (' . $mysqli->errno . ') ';
}

if($users->execute() == false) {
    echo 'Error: ' . $con->error;
}

$binding_results = $users->bind_result(        
    $FirstName,             
    $LastName,          
    $Picture
);
if (!$binding_results) {
    echo 'MySQL Connect Error in Query: (' . $mysqli->errno . ') ';
}

$users2 = $con->prepare("
SELECT DISTINCT
      Foo               
    , Bar               
    , FooBar 
FROM Bizz  
WHERE UserId = ?
");
if (!$users2) {
    echo 'MySQL Connect Error in Query: (' . $mysqli->errno . ') ';
}

$binding2 = $users2->bind_param('i', $GetUserId);
if (!$binding2) {
    echo 'MySQL Connect Error in Query: (' . $mysqli->errno . ') ';
}

if($users2->execute() == false) {
    echo 'Error: ' . $con->error;
}

$binding_results2 = $users2->bind_result(       
    $Foo,           
    $Bar,           
    $FooBar
);
if (!$binding_results2) {
    echo 'MySQL Connect Error in Query: (' . $mysqli->errno . ') ';
}

我可以在您的第一个查询中看到一个错误.您正在使用d.FirstName，其中表名是Details

I can see one mistake in your first query. you are using d.FirstName where as the table name is Details