PLEASE HELP ME TO FETCH LAST 3Weeks data in SQL

Question

I have to display 3 weeks data when the user selects one week.
In the front end i have start date and end date , after selecting the start and end date i have drop down list which will display the weeks . By passing weekid i need to fetch data for last 3 weeks, is this possible by passing only the week id. and what
if the user selects the last year as start date and current date as end date....
for example
if the user selects week -38
it should display data for week 38,37 and 36 . this is working if by decrementing the week by 1.
what if the user selects week 1, it should select the last 2 weeks of previous year as well. how will i do this by using week id...please help 

Answer 1

Please try following code in which you can change @increament value as you wish.
--sample DDL & DML
DECLARE @Table TABLE ( WeekId INT PRIMARY KEY );
INSERT @Table
VALUES ( 1 ), ( 2 ),( 3 ), ( 4 ),( 5 ),( 6 ), ( 7 ),( 8 );
--input parameters
DECLARE @WeekId INT = 1 ;
DECLARE @Increament INT = 2 ;
DECLARE @Mn INT ;
SELECT
@Mn = CASE
WHEN ( SELECT MAX(T2.WeekId) FROM @Table AS T2 WHERE T2.WeekId = T1.WeekId - @Increament ) IS NULL
THEN ( SELECT MAX(WeekId) FROM @Table ) - @Increament + T1.WeekId
ELSE ( SELECT MAX(T2.WeekId) FROM @Table AS T2 WHERE T2.WeekId = T1.WeekId - @Increament ) END
FROM
@Table AS T1
WHERE
T1.WeekId = @WeekId ;
IF @WeekId < @Mn
SELECT *
FROM @Table
WHERE WeekId <= @WeekId OR WeekId >= @Mn ;
ELSE
SELECT *
FROM @Table
WHERE WeekId BETWEEN @Mn AND @WeekId ;
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