Quartile in Oracle SQL - sql

Question

I have a table
table1
member
10010
10020
10030
10040
10050
10060
10070
10080
10090
10100
I want to divide the 10 rows into 4 buckets. I did the following:
select a.*, NTILE(4) over(order by member) as segment1 from table1 a
order by member;
But this gives me equal distribution in 4 buckets.
I would like to have decreasing 4 buckets. 1st one to have 40% then 30%, then 20%, then 10%.
Output should be:
member segment1
10010 1
10020 1
10030 1
10040 1
10050 2
10060 2
10070 2
10080 3
10090 3
10100 4
How can I achieve it using Oracle SQL?

Answer 1

One simple approach would be to use ROW_NUMBER along with a CASE expression:
WITH cte AS (
SELECT t.*, ROW_NUMBER() OVER (ORDER BY member) / COUNT(*) OVER () rn
FROM table1 t
)
SELECT
member,
CASE WHEN rn <= 0.4 THEN 1
WHEN rn <= 0.7 THEN 2
WHEN rn <= 0.9 THEN 3
ELSE 4 END AS segment1
FROM cte
ORDER BY
member;
Demo

Answer 2

I would use row_number() and count() for this:
select a.*,
(case when row_number() over (order by member) <= 0.4 * count(*) over () then 1
when row_number() over (order by member) <= 0.7 * count(*) over () then 2
when row_number() over (order by member) <= 0.9 * count(*) over () then 3
else 4
end) as segment
from table1 a
order by member;
Of course, you can also use ntile():
select a.*,
(case when ntile(10) over (order by member) <= 4 then 1
when ntile(10) over (order by member) <= 7 then 2
when ntile(10) over (order by member) <= 9 then 3
else 4
end) as segment
from table1 a
order by member;