T-SQL Query with SUM, DATEADD logic - tsql

Question

I’m looking for a query that can calculate the Calculation table from the Value table.
The query had to take the Date value, like ‘2017-03-01’ but I need to take the values from the records 2 months before, but it must be the record with the same ID. In this scenario It must take the values from 2017-03-01 , 2017-02-01, 2017-01-01 (993, 492, 312) and sum together (1,797) and store it in the 2017-03-01 record like below from the customer where CustomerID = 1001.
|1001 | 2017-02-01 | 492 | |
|1001 | 2017-03-01 | 993 | |
|1002 | 2017-01-01 | 838 | 1797 |
This need to be done of all records.
Of course, some record cannot go back minus 2 months, but those values can stay null.
I really don’t know to write this query.
Got some test queries to make some steps like:
SELECT SUM(Value) FROM TestTable WHERE Date BETWEEN Date AND DATEADD(month, -2, Date);
+------------+------------+-------+-------------+
| CustomerID | Date | Value | Calculation |
+------------+------------+-------+-------------+
| 1001 | 2016-08-01 | 123 | |
| 1001 | 2016-09-01 | 434 | |
| 1001 | 2016-10-01 | 423 | |
| 1001 | 2016-11-01 | 235 | |
| 1001 | 2016-12-01 | 432 | |
| 1001 | 2017-01-01 | 312 | |
| 1001 | 2017-02-01 | 492 | |
| 1001 | 2017-03-01 | 993 | |
| 1002 | 2017-01-01 | 838 | |
| 1002 | 2017-02-01 | 234 | |
| 1002 | 2017-03-01 | 453 | |
| 1002 | 2017-04-01 | 838 | |
| 1003 | 2017-01-01 | 746 | |
| 1003 | 2017-02-01 | 242 | |
| 1003 | 2017-03-01 | 432 | |
| 1004 | 2017-01-01 | 431 | |
| 1004 | 2017-02-01 | 113 | |
+------------+------------+-------+-------------+
I want my table like below
+------------+------------+-------+-------------+
| CustomerID | Date | Value | Calculation |
+------------+------------+-------+-------------+
| 1001 | 2016-08-01 | 123 | NULL |
| 1001 | 2016-09-01 | 434 | NULL |
| 1001 | 2016-10-01 | 423 | 980 |
| 1001 | 2016-11-01 | 235 | 1092 |
| 1001 | 2016-12-01 | 432 | 1090 |
| 1001 | 2017-01-01 | 312 | 979 |
| 1001 | 2017-02-01 | 492 | 1236 |
| 1001 | 2017-03-01 | 993 | 1797 |
| 1002 | 2017-01-01 | 838 | NULL |
| 1002 | 2017-02-01 | 234 | NULL |
| 1002 | 2017-03-01 | 453 | 1525 |
| 1002 | 2017-04-01 | 838 | 1525 |
| 1003 | 2017-01-01 | 746 | NULL |
| 1003 | 2017-02-01 | 242 | NULL |
| 1003 | 2017-03-01 | 432 | 1420 |
| 1004 | 2017-01-01 | 431 | NULL |
| 1004 | 2017-02-01 | 113 | NULL |
+------------+------------+-------+-------------+
I hope you can help me with this! 😉

Answer 1

--First Create Table
create table Testtable(
CustomerID int,
Date date,
Value int
)
--Insert test values
insert into Testtable VALUES(1001,'2016-08-01',123),
(1001,'2016-09-01',434),
(1001,'2016-10-01',423),
(1001,'2016-11-01',235),
(1001,'2016-12-01',432),
(1001,'2017-01-01',312),
(1001,'2017-02-01',492),
(1001,'2017-03-01',993),
(1002,'2017-01-01',838),
(1002,'2017-02-01',234),
(1002,'2017-03-01',453),
(1002,'2017-04-01',838),
(1003,'2017-01-01',746),
(1003,'2017-02-01',242),
(1003,'2017-03-01',432),
(1004,'2017-01-01',431),
(1004,'2017-02-01',113);
--Select Query
SELECT
CustomerID,
Date,
Value,
CASE WHEN (SELECT COUNT(*) FROM Testtable T4 WHERE T4.CustomerID = T3.CustomerID AND T4.Date < T3.Date) < 2 THEN NULL
ELSE Calculation END AS Calculation
FROM
(SELECT
*,
(SELECT SUM(T2.Value) FROM Testtable T2 WHERE T.CustomerID = T2.CustomerID AND T2.Date BETWEEN DATEADD(month,-2,T.Date) AND T.Date) AS Calculation
FROM Testtable T) AS T3

Answer 2

This might take some trial and error to get completely correct but I'll give it a shot, try below:
SELECT CustomerID
, Date
, Value
, Value +
(SELECT Value from table_name where CustomerID = x.CustomerID and Date =
DATEADD(m,-1,x.Date)) +
(SELECT Value from table_name where CustomerID = x.CustomerID and Date =
DATEADD(m,-2,x.Date)) as Calculation
FROM table_name x
Note that this will only work it the CustomerID/Date are a composite key in your table.
Hope this helps!