SQL Server: Sum of Calculated Row within N Months - sql-server

Question

I am new to SQL Server and have a question regarding summing over a calculated row with a conditional statement.
My data is organized as follows:
ID S_DATE END_DATE MNum CHG DateCHG
---------------------------------------------
1 1/26/2001 2/26/2001 7 NULL 1
1 2/27/2001 3/27/2001 8 1 1
1 3/28/2001 1/9/2003 9 1 21
1 1/10/2003 3/2/2004 11 2 14
1 3/3/2004 10/14/2004 10 -1 7
1 10/15/2004 6/22/2005 9 -1 8
1 6/23/2005 3/9/2008 8 -1 33
1 3/10/2008 1899-12-30 0 NULL -1299
2 9/23/1993 9/11/2000 3 NULL 84
2 1/1/1999 12/31/1998 3 0 -1
2 9/12/2000 11/13/2001 2 -1 14
2 11/14/2001 1899-12-30 0 NULL -1223
DateCHG is equal to the number of months between S_DATE & End_Date. I would like to find the SUM of CHG for each ID where the CHG occurs within 3 months of previous date.
Here is my current code (NOTE: Column headers are different from data above for formatting purposes. Also I cannot write to this database so only in Query format)
SELECT
*,
CASE
WHEN MratingNum = 0 OR
LAG(MratingNum) OVER (OVER BY MAST_ISSU_NUM, RATG_DATETIME) = 0 OR
MAST_ISSU_NUM <> LAG(MAST_ISSU_NUM) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME) --OR
--LAG(MratingNum) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME) < 12 OR --By Credit Rating
--LAG(MratingNum) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME) < 18
THEN NULL
ELSE CAST(MratingNum AS INT) - LAG(MratingNum) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME)
END AS CHG,
DATEDIFF(month, RATG_DATETIME, RATG_END_DATETIME) AS DateCHG
FROM
MOODYS_DRD.dbo.DEBT_RATG AS t1
LEFT JOIN
sandbox.dbo.RatingMap AS t2 ON t1.RATG_TXT = t2.MratingValue
WHERE
RATG_TYP_CD = 'LT'
ORDER BY
MAST_ISSU_NUM, RATG_DATETIME
So for example the output would look something like this:
ID S_DATE .... SumCHG
1 1/26/2001.... NULL
1 2/27/2001.... NULL
1 3/28/2001.... 2
1 1/10/2003.... NULL
1 3/3/2004 .... NULL
I'm assuming the best approach is to calculate a rolling sum of DateCHG where it is less than 3 and then SUM the CHG column? Thanks all!
EDIT: This is fairly complex so let me try another way of asking the question. For each record I want to look back and find the SUM of CHG within 3 months of the S_DATE. For 3/28/2001, this would include 2/01 and 1/01. The MNum went from 7 to 9 so the SUM of CHG would be 2. However from 3/04, there were no changes in the past 3 months so return NULL. I obviously want to do this per ID so don't want to overlap 3 months from ID 2 to 1. Hope this makes more sense now?

Answer 1

t0 and t are used for setting up the data.
with t0
as ( select *
from ( values ( 1, '1/26/2001', '2/26/2001', 7, null, 1),
( 1, '2/27/2001', '3/27/2001', 8, 1, 1),
( 1, '3/28/2001', '1/9/2003', 9, 1, 21),
( 1, '1/10/2003', '3/2/2004', 11, 2, 14),
( 1, '3/3/2004', '10/14/2004', 10, -1, 7),
( 1, '10/15/2004', '6/22/2005', 9, -1, 8),
( 1, '6/23/2005', '3/9/2008', 8, -1, 33),
( 1, '3/10/2008', '1899-12-30', 0, null, -1299),
( 2, '9/23/1993', '9/11/2000', 3, null, 84),
( 2, '1/1/1999', '12/31/1998', 3, 0, -1),
( 2, '9/12/2000', '11/13/2001', 2, -1, 14),
( 2, '11/14/2001', '1899-12-30', 0, null, -1223) ) t ( ID, S_DATE, END_DATE, MNum, CHG, DateCHG )
),
t as ( select t0.ID ,
cast(t0.S_DATE as date) S_DATE ,
cast(t0.END_DATE as date) END_DATE ,
t0.MNum ,
t0.CHG ,
t0.DateCHG
from t0
)
select case when Cnt >= 3 then p.CHG
end SumCHG,
*
from t
outer apply ( select sum(u.CHG) CHG ,
count(*) Cnt
from t u
where u.ID = t.ID
and u.S_DATE between dateadd(month, -3,
t.S_DATE)
and t.S_DATE
) p
order by t.ID ,
t.S_DATE;
Use CTE for your tables,
;with t as (
SELECT
*,
CASE
WHEN MratingNum = 0 OR
LAG(MratingNum) OVER (OVER BY MAST_ISSU_NUM, RATG_DATETIME) = 0 OR
MAST_ISSU_NUM <> LAG(MAST_ISSU_NUM) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME) --OR
--LAG(MratingNum) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME) < 12 OR --By Credit Rating
--LAG(MratingNum) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME) < 18
THEN NULL
ELSE CAST(MratingNum AS INT) - LAG(MratingNum) OVER (ORDER BY MAST_ISSU_NUM, RATG_DATETIME)
END AS CHG,
DATEDIFF(month, RATG_DATETIME, RATG_END_DATETIME) AS DateCHG
FROM
MOODYS_DRD.dbo.DEBT_RATG AS t1
LEFT JOIN
sandbox.dbo.RatingMap AS t2 ON t1.RATG_TXT = t2.MratingValue
WHERE
RATG_TYP_CD = 'LT'
)
select case when Cnt >= 3 then p.CHG
end SumCHG,
*
from t
outer apply ( select sum(u.CHG) CHG ,
count(*) Cnt
from t u
where u.ID = t.ID
and u.S_DATE between dateadd(month, -3,
t.S_DATE)
and t.S_DATE
) p
order by t.ID ,
t.S_DATE;