I need to format in such way to get number of years, months and their combination or 'No warranty', depending on whether the given product has a warranty or not. I tried with case + extract but it didn't work

select p.product_name, sum(o.quantity) as total_quantity,

case when p.warranty_period = interval '0-0' year to month then 'No
warranty'

when p.warranty_period < interval '0-11' year to month then
extract(month from p.warranty_period) || ' months'

when p.warranty_period < interval '21-0' year to month then -- make it
for all years, not only 1
extract(year from p.warranty_period) || ' years'

when p.warranty_period > interval '0-0' year to month then
extract(year from p.warranty_period) || ' years and ' || extract(month
from p.warranty_period)
|| ' months'

end WARRANTY from PRODUCT_INFORMATION p
join order_items o on p.product_id = o.product_id
group by p.product_name, p.warranty_period;