Using $this->input->post in a SQL Query Update

[eluser]internut[/eluser]
Hey all. Quick question. Why would this work:

Code:

$this->db->query("UPDATE settings SET setting='$_POST[admin_name]' WHERE name='admin_name'");

and this does not:

Code:

$this->db->query("UPDATE settings SET setting='$this->input->post(admin_name)' WHERE name='admin_name'");

do i need to set the var above the query call?

$admin_name = $this->input->post(admin_name);

Can i just use $this->input->post(admin_name) in the query update?