NTILE only for values different from zero

Question

I have a column with many zeros and I want to put only non-zero values into N groups of (approximately) equal sizes. All zero values should get group number 0. Is there an elegant way to do this?

My first approach was to use ntile_v2 from code below, but this way bin numbers dont't start with 1 and I don't get N bins.

with sample_data as
    (select 
        rownum as id,
        case when rownum <= 50 then 0 else rownum end as value
    from xmltable('1 to 100')
    )
select 
    id,
    value,
    ntile(50) over (order by value) as ntile_v1,
    case when value = 0 then 0 else ntile(50) over (order by value) end as ntile_v2
from sample_data
order by id;

One solution would be to put non-zero values into separate CTE, compute the tiles there, and join back:

with sample_data as
    (select 
        rownum as id,
        case when rownum <= 50 then 0 else rownum end as value
    from xmltable('1 to 100')
    )
, sample_data_not_zero as
    (select 
        id, 
        value, 
        ntile(50) over (order by value) as ntile_v3 
    from sample_data 
    where value <> 0
    )
select 
    sd.id,
    sd.value,
    nvl(sdnz.ntile_v3, 0) as ntile_v3
from 
    sample_data sd
    left outer join
    sample_data_not_zero sdnz on sd.id = sdnz.id
order by id;

Unfortunately I have to compute this for many different columns and I'm wondering whether there is a shorter solution.

Answer 1

You could partition the ntile based on zero vs non-zero, in addition to your current case expression:

case
  when value = 0 then 0
  else ntile(50) over (partition by case when value = 0 then 0 else 1 end order by value)
end as ntile_v3

That seems to get the same result as your union query.

db<>fiddle