Calcuate the number of weeks in a month

Question

I need a query to return the # of weeks ina  month for eg

June has MAY has 4 weeks, ie 5-1-07 thru 5-7-07 is week 1,

'5-6-07' and '5-10-07' is week 2 ETc.. hence i need my results to show as follows, but it needs to be automated for every month, ie the number of weeks in a month.

EG

when date between '5-1-07' and '5-5-07' then 'Week1'
when date between  '5-6-07' and '5-12-07' then week2'
when date between '5-13-07' and '5-19-07' then 'week3'

 

I need the results, above to be automated for each month..

 

 

Answer 1

You should consider the use of a Calendar table. (See this reference.)

 

A Calendar table is a very useful support object in most databases where it is often necessary to handle date related data.

Answer 2

I do have the calendar tbl. But that does not ahve the week of the month in it. I also looked at the reference u listed, I need the week of the month, ie between 1-5, not the week of the year.

Answer 3

I do have the calendar tbl. But that does not ahve the week of the month in it. I also looked at the reference u listed, I need the week of that  month, ie in May we have 5 weeks, so I need it sho show as week 1, week2 etc..ie between 1-5, not the week of the year.

Answer 4

 

 

Without knowing quite how you want to use it...here's an approach to start.

Code Snippet

 

declare @date datetime

set @date = getdate()

 

select 1 + (W + first.first_week_nbr) as MoWeekNbr

from dbo.Calendar

inner join

(

    select @date as seldate, first_week_nbr

    from dbo.calendar where dt = dateadd(d, -1*(day(@date)-1), @date)

) first

on first.seldate = @date

where dt = @date

 

Answer 5

It is easy to add additional columns to the Calendar table for your specific needs.

 

If you need a 'Week of the Month', then add a column and use an UPDATE to populate the data. It's not a complex algorithm...

Answer 6

Does the first week of each month ALWAYS start on the first?

Answer 7

Yes,  the first week of the month, always starts on the FIRST.

Answer 8

This code gives me erros such as Invalid column name 'first_week_nbr'. etc.. we dont have the same calendar table

Answer 9

IF you add a 'computed' WeekOfMonth column to your Calendar table, the following will create the proper values.

 

Code Snippet

ALTER TABLE Calendar
   ADD WeekOfMonth AS datepart( wk, dateadd( day, 0, datediff( day, dateadd( month, datediff( month, 0, [date] ), 0 ), [date] )))

 

Now you can use a JOIN with the Calendar table to find the WeekOfMonth and use that value in groupings, etc.

Answer 10

THis code does not return the rite result, for eg if the date is 2007-02-05, it falls under week 2.-BUT The code returns week1

select datepart( wk, dateadd( day, 0, datediff( day, dateadd( month, datediff( month, 0, '20070205' ), 0 ),
'20070205' )))

Answer 11

I asked you specifically, if

Does the first week of each month ALWAYS start on the first?

.

 

And you replied,

Yes,  the first week of the month, always starts on the FIRST.

 

Following that logic, the first through the 7th is in week one, 8th through 14th in week two, etc. Therefore '2007-02-05' would correctly fall in week one.

 

However, it seems like now your previous response may have mislead me. (And of course, I take responsibility for not asking my question in a more exacting form. I clearly see how the confusion exists.)

 

It appears that you may have meant that a week is from Sunday-Saturday (Calendar). And that any number of days falling within a calendar week (even if that calendar week contains the days of a different month) constitutues the 'first week of the month'.

 

My assumption was that a week was seven days.

 

Please clarify. What determines a Week? (Numerical or Calendar)

Answer 12

select day(getdate()) / 7 as [WeekOfMonth]

, convert(char(1),day(getdate()) / 7 ) + 'Week' as [MonthWeek]

--

select *

,day(<DateField>) / 7 as [WeekOfMonth]

, convert(char(1),day(<DateField>) / 7 ) + 'Week' as [MonthWeek]

from <TableName>

 

 

 

Answer 13

Rusag2,

 

Somehow, this just doesn't seem right... (using your suggested algorithms)

 

Code Snippet

Select
   Today = getdate(),
   WeekOfMonth = day(getdate()) / 7,
   MonthWeek = convert(char(1),day(getdate()) / 7 ) + 'Week'

 

Today                      WeekOfMonth MonthWeek
--------------------------- ----------- ---------
2007-06-25 19:46:26.130     3           3Week

 

It seems like today 'should be' in the forth (or fifth) week of the month...

 

Answer 14

here's another alternative, you can also make use of a calendar udf, here's my favorite calendar udf

 

 [edited]

CREATE  FUNCTION dbo.GetCalendarDates
(
 @StartDate smalldatetime
 , @EndDate smalldatetime
)
RETURNS @CalendarDates TABLE (
 Row int IDENTITY(1,1)
 , CalendarDate smalldatetime
 , [Day]   AS day( [CalendarDate] )
        , [Month] AS month( [CalendarDate] )
        , [Year]  AS year( [CalendarDate] )
        , YearDay AS datepart( dayofyear, [CalendarDate] )
 , DayOfWeek AS datepart( weekday, [CalendarDate] )
 , WeekOfYear AS datepart( week, [CalendarDate] )
 , DateFirst AS @@DATEFIRST
 , WeekOfMonth int
 , NumOfWeeks int
 , WeekStart smalldatetime
 , WeekEnd smalldatetime
)
AS
BEGIN
 DECLARE @StartOfMonth smalldatetime
 DECLARE @EndOfMonth smalldatetime

 SET @StartOfMonth = CONVERT(varchar(2),MONTH(@StartDate)) + '/1/' + CONVERT(varchar(4),YEAR(@StartDate))
 SET @EndOfMonth = CONVERT(varchar(2),MONTH(@EndDate)) + '/1/' + CONVERT(varchar(4),YEAR(@EndDate))
 SET @EndOfMonth = DATEADD(day,-1,DATEADD(month,1,@EndOfMonth))

 WHILE @StartOfMonth <= @EndOfMonth
  BEGIN
   
   INSERT
   INTO @CalendarDates
   SELECT CONVERT(varchar(10),@StartOfMonth,101), 1, 1, CONVERT(varchar(10),@StartOfMonth,101), CONVERT(varchar(10),@StartOfMonth,101)

   SET @StartOfMonth = DATEADD(d,1,@StartOfMonth)
  END
 
 

 UPDATE a
 SET WeekOfMonth = WeekOfYear - MinWeek
 FROM @CalendarDates a INNER JOIN
  (
   SELECT [Year]
    , [Month]
    , MIN(WeekOfYear) - 1 AS MinWeek
   FROM @CalendarDates
   GROUP BY
    [Year]
    , [Month]
  ) b ON a.[Year] = b.[Year]
   AND a.[Month] = b.[Month]
 
 UPDATE a
 SET WeekStart = b.WeekStart
  , WeekEnd = b.WeekEnd
  , NumOfWeeks = b.NumOfWeeks
 FROM @CalendarDates a INNER JOIN
  (
   SELECT [Year]
    , [Month]
    , WeekOfMonth
    , MIN(CalendarDate) AS WeekStart
    , MAX(CalendarDate) AS WeekEnd
    , COUNT(Row) AS NumOfWeeks
   FROM @CalendarDates
   GROUP BY
    [Year]
    , [Month]
    , WeekOfMonth
  ) b ON a.[Year] = b.[Year]
   AND  a.[Month] = b.[Month] 
   AND a.WeekOfMonth = b.WeekOfMonth

 

 UPDATE a
 SET NumOfWeeks = b.NumOfWeeks
 FROM @CalendarDates a INNER JOIN
  ( SELECT [Year]
    , [Month]
    , Max(WeekOfMonth) AS NumOfWeeks
    FROM @CalendarDates
   GROUP BY
    [Year]
    , [Month]
  ) b ON a.[Year] = b.[Year]
   AND  a.[Month] = b.[Month] 

 

 DELETE 
 FROM @CalendarDates
 WHERE CalendarDate NOT BETWEEN @StartDate AND @EndDate

RETURN
END

 

ex.

 

declare @to smalldatetime
declare @from smalldatetime
declare @thedate smalldatetime

 

set @to = '06/01/2007'
set @from = '07/30/2007'
set @thedate = '06/25/2007'

 

[edited] 

select distinct @thedate, a.WeekOfMonth, a.WeekStart, a.WeekEnd, 'Week ' + convert(varchar(1),a.WeekOfMonth)
from dbo.GetCalendarDates(@to,@from) a

Answer 15

 

 

Oops, buggered that.

Try this:

Code Snippet

 

declare @date datetime

set @date = getdate()

 

select 1 + (W + first.first_week_nbr) as MoWeekNbr

from dbo.Calendar

inner join

(

    select @date as seldate, W as first_week_nbr

    from dbo.calendar where dt = dateadd(d, -1*(day(@date)-1), @date)

) first

on first.seldate = @date

where dt = @date

 

Answer 16

Yes Arnie, you are rite. TOday ie 2007-6-26, should really be in the 5th week. I applogize for not clarifying earlier.. Sorry abt that.

Answer 17

Yes , thats rite- the week is from Sunday thru Saturday.. ie eg 2007-06-01, though falls on a Friday, it should show as WEEK1 , For June.

Answer 18

Try:

 

declare @d datetime

 

set @d = '20070515'

 

select datediff(week, convert(varchar(6), @d, 112) + '01', @d) + 1

go

 

 

AMB

Answer 19

Tarana,

 

It appears that Alejandro's (hunchback/AMB) suggested algorithm works as you desire.

 

Try using it to populate your calendar table.

 

Alejandro -very nice, simple and elegant. Counts the number of week 'boundaries' between the first of the month and the supplied date.

 

(Note: Check the DATEFIRST setting to verify what is the first day of the week.)

 

 

Answer 20

this code is very good if the week starts with sunday. I need the same thing, but i need the week to start with monday. can u help me? thanks