How to select top 1 vaue in mysql

<?php
if($_SERVER['REQUEST_METHOD']=='POST'){

include 'DatabaseConfig.php';

 $con = mysqli_connect($HostName,$HostUser,$HostPass,$DatabaseName);




 $CheckSQL = "SELECT * FROM table ORDER BY rank DESC LIMIT 10";
 
 $check = mysqli_fetch_array(mysqli_query($con,$CheckSQL));
 if(isset($check)){
 echo 'Error';
//$Sql_Query = "INSERT INTO users (id) values ('$F_name'+$check)";
 }
else{ 
$Sql_Query = "INSERT INTO complain (complainno) values ('$check')";

 if(mysqli_query($con,$Sql_Query))
{
 echo 'Registration Successfully';
}
else
{
 echo 'Something went wrong';
 }
 }
}
 mysqli_close($con);
?>