samples_by_age.sql

explain analyze
select 
  count(age) as samples,
case
  when age < 20 then 2000
  when (age >= 20) and (age < 30) then 2030
  when (age >= 30) and (age < 40) then 3040
  when (age >= 40) and (age < 50) then 4050
  when (age >= 50) and (age < 60) then 5060
  when age >= 60 then 6000
else ''
end as age_category
from samples
group by age_category;