将mysql结果放在一个php数组中，像这样？

To get an array like this array("123","456","789"); I use the code:

$Regids = mysql_query("SELECT regid FROM $tabel WHERE active = '1'");
while($row = mysql_fetch_array($Regids))
{
    $result_array[] = "\"".$row['regid']."\"";
}
$regIDs = implode(',', $result_array);
$registrationIDs = array($regIDs); // array("123","456","789");

but I would expect PHP/mySQL has a simpler/faster solution for this?

try this .. use Group concat in query ...

$Regids = mysql_fetch_array(mysql_query("SELECT GROUP_CONCAT(regid) as regids FROM $tabel WHERE active = '1'"));
echo $Regids[0]['regids']; // 123,456,789

for getting result "123","456","789" try this

$Regids = mysql_fetch_array(mysql_query("SELECT GROUP_CONCAT('\"',CONCAT(regid),'\"') as regids FROM $tabel WHERE active = '1'"));
    echo $Regids[0]['regids']; // "123","456","789"

I doubt that your code produces the result you want.

// assuming the this query produces 123,456,789
$Regids = mysql_query("SELECT regid FROM $tabel WHERE active = '1'");
// $row contains: array("123")
while($row = mysql_fetch_array($Regids))
{
    $result_array[] = "\"".$row['regid']."\"";
}
// $result_array now contains: array("\"123\"", "\"456\"", "\"798\"");
$regIDs = implode(',', $result_array);
// $regIDS now contains a single string: "\"123\",\"456\",\"798\"";
$registrationIDs = array($regIDs);
// registrationIDs now is an array containing a single string: array("\"123\",\"456\",\"798\"");

If you really need an array that looks like this: array("123","456","789"); it is much simpler.

$Regids = mysql_query("SELECT regid FROM $tabel WHERE active = '1'");
while($row = mysql_fetch_array($Regids))
    $registrationIDs[] = $row['regid'];

and that's all.

If your mysql result contains the number as an integer instead of an string you can convert it like this:

$Regids = mysql_query("SELECT regid FROM $tabel WHERE active = '1'");
while($row = mysql_fetch_array($Regids))
    $registrationIDs[] = strval($row['regid']);

Also, keep in mind that the mysql_* functions are becoming deprecated. Don't start new code with it and make plans to port your existing code to mysqli_* or PDO.

You can use PDO implementation. At first sight, it may be more difficult to understand, but once you get used to it, it reveals to be really powerful and handy (IMHO! One year ago i switched to it and i love it)!

For your example, the PDO implementation would be like this:

/*CONNECT TO DB, FIRST. $dbh contains a handler to the current DB connection*/
$stmt = $dbh->prepare("SELECT regid FROM table WHERE active = '1'");
$stmt->execute();
$Regids = $stmt->fetchAll(PDO::FETCH_COLUMN,0);

There are many formatting options you can specify, like

PDO::FETCH_COLUMN

PDO::FETCH_ASSOC

and more...These options will allow you to get the array formatted as you prefer. As you can see i got the result in just 3 simple rows.

EDIT

Note: you are not escaping PHP variables before inserting them in your Query, and your code may suffer SQL INJECTION. Be careful!! Here is a simple guide to prevent it. (In my code, just to be clear, i avoided the problem by just putting the table name instead of $table, just to show simply how to get the result you wanted.)