For some further operations, I need to quickly get the MAX(UserId) of a table containing users. Is it safe to do the following?

$max_user = sqlsrv_fetch_array(sqlsrv_query($connection, "SELECT MAX(UserID) FROM z_users;"))[0];

I mean without using a loop like while ($row = sqlsrv_fetch_array($result, SQLSRV_FETCH_ASSOC)) {

Also, I noticed that using the code I wrote above returns an array with two elements: one with index 0 and another without an index but with the same value.

Like Array ( [0] => 1211 [] => 1211 )

Why is this happening?