plsql if control different calculation - if-statement

Question

I am using PLSQL to realize some of the function below.
I have the table which have piece level data with each piece weight. Basically I want to realize the following function:
if piece weight is over 1 LB. groupby ceil(weight) (next LB)
if piece weight is less 1 LB groupby cell(weight*16) ( Next OZ)
I am just curious how can I realize that in plsql. I feel I need to have the if statement. But I am not sure how to do that.
(Weight is already an variable in that table, do I need to declare here?)
begin
if weight <1 then
select ceil(weight*16),sum(weight)
from ops_owner.track_mail_item
where manifestdate = '24-aug-2016'
group by ceil(weight*16)
else select ceil(weight),sum(weight)
from ops_owner.track_mail_item
where manifestdate = '24-aug-2016'
end if,
end;
Thank you very much!

Answer 1

I would adjust the weight value in an inline view, I think.
select
ceil(adjusted_weight),
sum(adjusted_weight)
from
(
select
case
when weight < 1 then weight * 16
else weight
end adjusted_weight
from
ops_owner.track_mail_item
where
manifestdate = '24-aug-2016'
)
group by
ceil(adjusted_weight);