Given the following data:
sequence | amount
1 100000
1 20000
2 10000
2 10000
I'd like to write a sql query that gives me the sum of the current sequence, plus the sum of the previous sequence. Like so:
sequence | current | previous
1 120000 0
2 20000 120000
I know the solution likely involves windowing functions but I'm not too sure how to implement it without subqueries.
select
seq,
amount,
lag(amount::int, 1, 0) over(order by seq) as previous
from (
select seq, sum(amount) as amount
from sa
group by seq
) s
order by seq
If your sequence is "sequencial" without holes you can simply do:
SELECT t1.sequence,
SUM(t1.amount),
(SELECT SUM(t2.amount) from mytable t2 WHERE t2.sequence = t1.sequence - 1)
FROM mytable t1
GROUP BY t1.sequence
ORDER BY t1.sequence
Otherwise, instead of t2.sequence = t1.sequence - 1 you could do:
SELECT t1.sequence,
SUM(t1.amount),
(SELECT SUM(t2.amount)
from mytable t2
WHERE t2.sequence = (SELECT MAX(t3.sequence)
FROM mytable t3
WHERE t3.sequence < t1.sequence))
FROM mytable t1
GROUP BY t1.sequence
ORDER BY t1.sequence;
You can see both approaches in this fiddle
