How do I create a custom Year/Week field in SQL Server? - sql-server

Question

I'm trying to extend a CalendarDate table in one of our systems because the initial table only had dates up to the end of 2019. (I know...)
The issue is that one of the fields is a week field for our client that is in the format YYYYXX, where XX is a counter of week (ie 01 - 52).
The problem I am encountering is that there is a corresponding DayOfWeek field where Saturday is 1, and the week in the problem column increments on a Saturday, whereas in SQL Server it seems that DATEPART(WEEK, #Date) increments on a Sunday.
Using a temporary table of dates from today until 2030, is there any way I can compute this column?
One caveat is that the column must contain 52 full weeks per year. This means, for example, that the week 202001 in this column actually started on 2019-12-28, so I cannot simply get the year component from DATEPART(YEAR, #date)
Here is what I have so far (#TempDates is just a table with list of dates from today onward):
SELECT
10 AS TrackingGroupID,
CAST([Date] AS DATETIME) AS CalendarDate,
NULL AS RetailerWeek,
CAST(CAST(DATEPART(YEAR, Date) AS VARCHAR(4))
+ RIGHT('000' + CONVERT(VARCHAR(3), DATEPART(DAYOFYEAR, Date)), 3) AS INT) AS DateID,
UPPER(SUBSTRING(DATENAME(WEEKDAY, Date), 1, 3)) AS DayOfWeek,
CASE UPPER(SUBSTRING(DATENAME(WEEKDAY, Date), 1, 3))
WHEN 'SAT' THEN 1
WHEN 'SUN' THEN 2
WHEN 'MON' THEN 3
WHEN 'TUE' THEN 4
WHEN 'WED' THEN 5
WHEN 'THU' THEN 6
WHEN 'FRI' THEN 7
END AS DayOfWeekID,
-- This is the column that needs fixing
CAST(CAST(DATEPART(YEAR, Date) AS VARCHAR(4))
+ RIGHT('00' + CONVERT(VARCHAR(2), DATEPART(WEEK, Date)), 2) AS INT) AS RetailerWeek2
FROM
#TempDates

Answer 1

I use this code to create date dimension.
This contains the week for every day.
You can generate the week as you wish.
/*Creación de la tabla*/
create table Dimensiones.Fecha
(
FechaSK int not null,
Fecha date not null,
Año smallint not null,
Trimestre smallint not null,
Mes smallint not null,
Semana smallint not null,
Dia smallint not null,
DiaSemana smallint not null,
NTrimestre char(12) not null,
NMes char(15) not null,
NMes3L char(3) not null,
NSemana char(10) not null,
NDia char(6) not null,
NDiaSemana char(10) not null
constraint PK_DIM_TIEMPO PRIMARY KEY CLUSTERED
(
Fecha asc
)
)
/*Script de carga*/
DECLARE #FechaDesde as smalldatetime, #FechaHasta as smalldatetime
DECLARE #FechaAAAAMMDD int
DECLARE #Año as smallint, #Trimestre char(2), #Mes smallint
DECLARE #Semana smallint, #Dia smallint, #DiaSemana smallint
DECLARE #NTrimestre char(12), #NMes char(15)
DECLARE #NMes3l char(3)
DECLARE #NSemana char(10), #NDia char(6), #NDiaSemana char(10)
--Set inicial por si no coincide con los del servidor
SET DATEFORMAT dmy
SET DATEFIRST 1
BEGIN TRANSACTION
--Borrar datos actuales, si fuese necesario
TRUNCATE TABLE dimensiones.fecha
--Rango de fechas a generar: del 01/01/1990 al 31/12/Año actual+2
SELECT #FechaDesde = CAST('19900101' AS smalldatetime)
--SELECT #FechaHasta = CAST(CAST(YEAR(GETDATE())+2 AS CHAR(4)) + '1231' AS smalldatetime)
WHILE (#FechaDesde <= #FechaHasta) BEGIN
SELECT #FechaAAAAMMDD = YEAR(#FechaDesde)*10000+
MONTH(#FechaDesde)*100+
DATEPART(dd, #FechaDesde)
SELECT #Año = DATEPART(yy, #FechaDesde)
SELECT #Trimestre = DATEPART(qq, #FechaDesde)
SELECT #Mes = DATEPART(m, #FechaDesde)
SELECT #Semana = DATEPART(wk, #FechaDesde)
SELECT #Dia = RIGHT('0' + DATEPART(dd, #FechaDesde),2)
SELECT #DiaSemana = DATEPART(DW, #FechaDesde)
SELECT #NMes = DATENAME(mm, #FechaDesde)
SELECT #NMes3l = LEFT(#NMes, 3)
SELECT #NTrimestre = 'Trimestre ' + CAST(#Trimestre as CHAR(1))
SELECT #NSemana = 'Sem ' +CAST(#Semana AS CHAR(2)) + '/' + RIGHT(RTRIM(CAST(#Año as CHAR(4))),2)
SELECT #NDia = CAST(#Dia as CHAR(2)) + ' ' + RTRIM(#NMes)
SELECT #NDiaSemana = DATENAME(dw, #FechaDesde)
INSERT INTO Dimensiones.Fecha
(
FechaSK,
Fecha,
Año,
Trimestre,
Mes,
Semana,
Dia,
DiaSemana,
NTrimestre,
NMes,
NMes3L,
NSemana,
NDia,
NDiaSemana
) VALUES
(
#FechaAAAAMMDD,
#FechaDesde,
#Año,
#Trimestre,
#Mes,
#Semana,
#Dia,
#DiaSemana,
#NTrimestre,
#NMes,
#NMes3l,
#NSemana,
#NDia,
#NDiaSemana
)
--Incremento del bucle
SELECT #FechaDesde = DATEADD(DAY, 1, #FechaDesde)
END
COMMIT TRANSACTION

Answer 2

If you set the DATEFIRST to 6 then a week starts on saturday.
Then by using a CASE WHEN the year & week can be adjusted.
...
CAST(
CASE
WHEN DATEPART(week, [Date]) > 52
THEN (100*(YEAR([Date])+1))+1
ELSE (100* YEAR([Date])) + DATEPART(week, [Date])
END AS VARCHAR(6)) as RetailerWeek2
...
Example:
SET DATEFIRST 6; -- 6: Saturday
SELECT ##DATEFIRST AS datefirst;
SELECT [Date]
, DATEPART(week, [Date]) as WeekNr
, DATEPART(dw, [Date]) as WeekdayNr
, CAST(
CASE
WHEN DATEPART(week, [Date]) > 52
THEN (100*(YEAR([Date])+1))+1
ELSE (100* YEAR([Date])) + DATEPART(week, [Date])
END AS VARCHAR(6)) as AdjustedYearWeek
FROM (VALUES
(CAST('2019-12-28' AS DATE)),
(CAST('2020-01-01' AS DATE)),
(CAST('2020-12-31' AS DATE))
) q([Date]);
GO
| datefirst |
| :-------- |
| 6 |
Date | WeekNr | WeekdayNr | AdjustedYearWeek
:------------------ | -----: | --------: | :---------------
28/12/2019 00:00:00 | 53 | 1 | 202001
01/01/2020 00:00:00 | 1 | 5 | 202001
31/12/2020 00:00:00 | 53 | 6 | 202101
db<>fiddle here