Is there a way to partition by incremental series in Postgressql? - sql

Question

In postgressql is there a way to attain the result below by using partition by or any other way?
last_name year increment partition
Doe 2000 1 1
Doe 2001 2 1
Doe 2002 3 1
Doe 2003 -1 2
Doe 2004 1 3
Doe 2005 2 3
Doe 2006 3 3
Doe 2007 -1 4
Doe 2008 -2 4

Answer 1

SELECT last_name,
year,
increment,
SUM(CASE WHEN increment < 0 THEN 1 ELSE 0 END) OVER (PARTITION BY last_name ORDER BY year) AS partition
FROM your_table
ORDER BY last_name, year;

Answer 2

It seems that you want to group the consecutive positive/ negative values together, one option is to use a difference between two row_number functions, this will make the partition but with unordered group numbers.
select *,
row_number() over (partition by last_name order by year) -
row_number() over (partition by last_name,
case when increment>=0 then 1 else 2 end order by year) as prt
from tbl
order by last_name, year
If you want the partitions in order (1, 2, 3...) you could try another approach using lag and running sum as the following:
select last_name, year, increment,
1 + sum(case when sign(increment) <> sign(pre_inc) then 1 else 0 end) over
(partition by last_name order by year) as prt
from
(
select *,
lag(increment, 1 , increment) over
(partition by last_name order by year) pre_inc
from tbl
) t
order by last_name, year
See demo

Answer 3

If the increment column does encrease over the column year, it will be marked as 1; otherwise, it will be marked as 0. Then, we group the successive data using "LAG", regardless of whether the increment is positive or negative.
with cte as (
select * ,
row_number() over (partition by last_name order by year) as row_num,
case when increment >= LAG(increment,1,0) over (partition by last_name order by year)
then 1 else 0 end rank_num
from mytable
),
cte2 as (
select *, LAG(rank_num,1,1) over (partition by last_name order by year) as pre
from cte
order by year
)
select last_name, year, increment, 1+sum(case when pre <> rank_num then 1 else 0 end) over
(partition by last_name order by year) as partition
from cte2;