The request parameter does not behave as expected

I use the query parameter :orderto pass the order argument of my function. Unfortunately, this does not affect the output.

The debug output of the query shows that the argument orderis parsed correctly:

Parameter #2(cf_sql_varchar) = posts.createdAt ASC

However, the output is still irrelevant. If I hardcode the argument ( ORDER BY ..., #arguments.order#), it works fine.

Any ideas?

public any function getPost(required numeric postId, string order)
{
    switch(arguments.order)
    {
        case "new":
            arguments.order = "posts.createdAt DESC";
            break;
        case "old": 
            arguments.order = "posts.createdAt ASC";
            break;
        default:
            arguments.order = "posts.score DESC";
    }

    local.post = new Query(dataSource=variables.wheels.class.connection.datasource);
    local.post.setSql("
        SELECT *
        FROM
        WHERE posts.id = :postId OR posts.parentId = :postId
        ORDER BY posts.postTypeId ASC, :order"
    );

    local.post.addParam(name="postId", cfsqltype="cf_sql_integer", value=arguments.postId, maxlength=10);
    local.post.addParam(name="order", cfsqltype="cf_sql_varchar", value=arguments.order, maxlength=20);
    local.post = local.post.execute().getResult();

    return local.post;

}