Baseret på oplysningerne i den artikel, du linkede til, burde dette virke:
update giveaways set winner='1'
where Id = (select Id from (select max(Id) as id from giveaways) as t)
Baseret på oplysningerne i den artikel, du linkede til, burde dette virke:
update giveaways set winner='1'
where Id = (select Id from (select max(Id) as id from giveaways) as t)