How to use lead lag function in oracle - sql

Question

I have written some query to get my resultant result as below :
Note: I have months starting from jan-2016 to jan-2018.
There are two types, either 'hist' or 'future'
Resultant dataset :
In this example : let consider combination of id1+id2+id3 as 1,2,3
type month id1 id2 id3 value
hist jan-17 1 2 3 10
hist feb-17 1 2 3 20
future jan-17 1 2 3 15
future feb-17 1 2 3 1
hist mar-17 1 2 3 2
future apr-17 1 2 3 5
My calculation logic depends on the quarter number of month .
For eg . for month of january(first month of quarter) i want the value to be : future of jan + future value of feb + future value of march .
so for jan-17 , output should be : 15+1 + 0(for march there is no corresponding future value)
for the month of feb (2nd month of quarter), value should be : hist of jan + future of feb + future of march i.e 10+1+0(future of march is not available)
Similarly for the month of march , value should be : history of jan + history of feb + future of march i.e 10+20+0(frecast of march no present) .
similarly for april,may.june(depending on quarter number of month)
I am aware of the lead lag function , but I am not able to apply it here
Can someone please help

Answer 1

I would not mess with lag, this can all be done with a group by if you convert your dates to quarters:
WITH
dset
AS
(SELECT DATE '2017-01-17' month, 5 VALUE
FROM DUAL
UNION ALL
SELECT DATE '2017-02-17' month, 6 VALUE
FROM DUAL
UNION ALL
SELECT DATE '2017-03-25' month, 7 VALUE
FROM DUAL
UNION ALL
SELECT DATE '2017-05-25' month, 4 VALUE
FROM DUAL)
SELECT SUM (VALUE) value_sum, TO_CHAR (month, 'q') quarter, TO_CHAR (month, 'YYYY') year
FROM dset
GROUP BY TO_CHAR (month, 'q'), TO_CHAR (month, 'YYYY');
This results in:
VALUE_SUM QUARTER YEAR
18 1 2017
4 2 2017
We can use an analytic function if you need the result on each record:
SELECT SUM (VALUE) OVER (PARTITION BY TO_CHAR (month, 'q'), TO_CHAR (month, 'YYYY')) quarter_sum, month, VALUE
FROM dset
This results in:
QUARTER_SUM MONTH VALUE
18 1/17/2017 5
18 2/17/2017 6
18 3/25/2017 7
4 5/25/2017 4
Make certain you include year, you don't want to combine quarters from different years.

Answer 2

Well, as said in one of the comments.. the trick lies in another question of yours & the corresponding answer. Well... it goes somewhat like this..
with
x as
(select 'hist' type, To_Date('JAN-2017','MON-YYYY') ym , 10 value from dual union all
select 'future' type, To_Date('JAN-2017','MON-YYYY'), 15 value from dual union all
select 'future' type, To_Date('FEB-2017','MON-YYYY'), 1 value from dual),
y as
(select * from x Pivot(Sum(Value) For Type in ('hist' as h,'future' as f))),
/* Pivot for easy lag,lead query instead of working with rows..*/
z as
(
select ym,sum(h) H,sum(f) F from (
Select y.ym,y.H,y.F from y
union all
select add_months(to_Date('01-JAN-2017','DD-MON-YYYY'),rownum-1) ym, 0 H, 0 F
from dual connect by rownum <=3 /* depends on how many months you are querying...
so this dual adds the corresponding missing 0 records...*/
) group by ym
)
select
ym,
Case
When MOD(Extract(Month from YM),3) = 1
Then F + Lead(F,1) Over(Order by ym) + Lead(F,2) Over(Order by ym)
When MOD(Extract(Month from YM),3) = 2
Then Lag(H,1) Over(Order by ym) + F + Lead(F,1) Over(Order by ym)
When MOD(Extract(Month from YM),3) = 3
Then Lag(H,2) Over(Order by ym) + Lag(H,1) Over(Order by ym) + F
End Required_Value
from z