SQL Server - add/cumulative for last 3 days [closed] - sql-server

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Table 1
Amount
10
20
25
40
50
60
70
80
90
100
110
120
130
Write an sql query to get output as
07/11/2018 10
07/12/2018 20
07/13/2018 25 55
07/14/2018 40 85
07/15/2018 50 115
07/16/2018 60 150
07/17/2018 70 180
07/18/2018 80 210
07/19/2018 90 240
07/20/2018 100 270
07/21/2018 110 300
07/22/2018 120 330
07/23/2018 130 360
So I want to add the last 3 days amount values and get the sum.

Answer 1

The LAG window function is what you need. It allows you to access the value in a column from a previous row. The format is LAG([Column], [Row Offset], [Default]), so this example adds the value from the current row to the value 2 rows back and the value 1 row back.
DECLARE #t TABLE (dt DATE, c INT)
INSERT INTO #t VALUES
('07/11/2018',10),
('07/12/2018',20),
('07/13/2018',25),
('07/14/2018',40),
('07/15/2018',50),
('07/16/2018',60),
('07/17/2018',70),
('07/18/2018',80),
('07/19/2018',90),
('07/20/2018',100),
('07/21/2018',110),
('07/22/2018',120),
('07/23/2018',130)
SELECT dt, c,
c + LAG(c, 2) OVER (ORDER BY dt) + LAG(c, 1) OVER (ORDER BY dt)
FROM #t
ORDER BY dt
Returns:
dt c
2018-07-11 10 NULL
2018-07-12 20 NULL
2018-07-13 25 55
2018-07-14 40 85
2018-07-15 50 115
2018-07-16 60 150
2018-07-17 70 180
2018-07-18 80 210
2018-07-19 90 240
2018-07-20 100 270
2018-07-21 110 300
2018-07-22 120 330
2018-07-23 130 360

Answer 2

I'm not going to give you a full answer here, as you've not responded to my comments. Thus I'm going to give you a partial answer, so that you can work out how to do this yourself.
When working with SUM, you also have access to the OVER clause. In 2012+ (which I assume you're using, as 2008 is effectively out of support now, and anything before is completely unsupported) you have access to the ROWS BETWEEN clause in OVER.
For example:
WITH N AS (
SELECT *
FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL)) V(N)),
Tally AS (
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS I
FROM N N1
CROSS JOIN N N2)
SELECT I,
SUM(I) OVER (ORDER BY I
ROWS BETWEEN CURRENT ROW AND 3 FOLLOWING) AS SomeSum
FROM Tally
ORDER BY I;
This example calculates the SUM of the current row, and the 3 following rows afterwards. So, for I = 1, that's SUM(1,2,3,4) = 10.
This can all be found in the documentation: SUM (Transact-SQL). SELECT - OVER Clause (Transact-SQL)