About ORDER BY questions

About the order by question
Something like this.

Say Www.xxx.com/index.php?id=5&order=zhucetime.

er =$_get[' order '];
$id =$_get[' id '];


$sqltext = "SELECT * from table where n_pid= '". $id. "' ORDER BY '". er. "' ASC ';





How do I achieve the first click by ASC sort the second click followed by the Desc sort of continuous cycle switching ah?

How do I achieve the first click by ASC sort the second click followed by the Desc sort of continuous cycle switching ah?

------Solution--------------------

------Solution--------------------
$_session[' direction '] = = ' desc ')
{
   $_session[' direction ' = ' ASC ';
}
Else
{
   $_session[' direction '] = ' desc ';
}

$sql = "SELECT * from table where n_pid= '". $id. "'  ORDER by  ". er."  . $_session[' direction '];

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