QT5/QSql bindValue query doesn't work

Question

I have a query made with QSql

query.prepare("SELECT id,title,content FROM posts ORDER BY :field :order LIMIT :limit OFFSET :offset");
query.bindValue(":field",QVariant(field));
query.bindValue(":order",order);
query.bindValue(":limit",limit);
query.bindValue(":offset",offset);

I use order value as "DESC" but it doesn't work properly. But , when I do

query.prepare("SELECT id,title,content FROM posts ORDER BY "+field+"  "+order+" LIMIT :limit OFFSET :offset");
query.bindValue(":limit",limit);
query.bindValue(":offset",offset);

it works fine and I don't know why. The values are of the same type ( QString and int ). Any suggestions ?

Thanks.