Converting a MySQL question mark parameter to a named parameter for reuse in the same query

example.sql

select
	(@param1 := ?),
	value,
	timestamp,
	Field.name,
	Site.id

from
	Field_Value

inner join
	Site_Field
on
	id_Site_Field = Site_Field.id

inner join
	Site
on
	id_Site = Site.id

where
	(@param1 is null
	or Site.id = @param1)

order by
	id desc

limit 10