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How to get the Nth weekday of a month from a calendar table

Hi

I have a calendar table (seems to be the best practice for other stuff I'm doing)

I have a need to select the top n records for the nth day in a month

SO from today if I need the top 5 second Tuesdays I would expect to get

10 Feb
10 Mar
14 Apr
12 May
9 June

In my table I have the day number ie a Monday is 2, and month ie feb is a 2 also.

If this cant be done in a query I could add another row to the table of day ordinal in a month, then the query would be simple, but how would I do that, The calendar currently holds 10 years worth of dates.

I'm using SQL server 2008

Andy
0
Andy Green
Asked:
Andy Green
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2 Solutions
 
Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
You need to post the syntax of your calendar table, as it will depend on what information you currently have.

Of the top of my head, it would seem that you want something like

With myTable as (
Select MyDate, MyWeekDay, ROW_NUMBER() OVER(Partition by Month Order By MyDate) as MyRowNumber
From myCalendarTable
WHERE MyWeekDay = 2)

Select MyDate
Where MyRowNumber = 2

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but it depends on your calendar table.
0
 
Andy GreenAuthor Commented:
Here you go:

CREATE TABLE [dbo].[zCalendar](
      [dt] [smalldatetime] NOT NULL,
      [isWorkday] [bit] NULL,
      [isHoliday] [bit] NULL,
      [Y] [smallint] NULL,
      [FY] [smallint] NULL,
      [Q] [tinyint] NULL,
      [M] [tinyint] NULL,
      [D] [tinyint] NULL,
      [DW] [tinyint] NULL,
      [monthname] [varchar](9) NULL,
      [dayname] [varchar](9) NULL,
      [W] [tinyint] NULL)

D is the day ( as in date day and the DW is the day in week IE 1 is a Monday.

A
0
 
Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
Then try this:

With myTable as (
Select D, DW, ROW_NUMBER() OVER(Partition by M Order By D) as MyRowNumber
From zCalendar
WHERE DW = 2)

Select D
Where MyRowNumber = 2

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0
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Andy GreenAuthor Commented:
Will do Phillip thank you.

The more I think about this  would it be more efficient to hold the position of the day in a month in another column, would make the SQL easier

Andy
0
 
Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
Then it would be Day between 8 and 14 and DW = 2
0
 
Andy GreenAuthor Commented:
I need 2 parameters, the day number (1-7) and its position in the month (1 First - 5 Last which could also be 4)

My query would be where day = 2 and ordinal = 2 would return the second Tuesday, but how to populate the column in the table?

Andy
0
 
PortletPaulCommented:
add a field to your table, below I used [dw_ordinal]

update zCalendar
set dw_ordinal = xtra.rn
from zCalendar
join (
  select dt, row_number() over(partition by y, m, dw order by dt) as rn
  from zCalendar
  ) xtra on zCalendar.dt = xtra.dt
;

select
      dt, y, m, dw, dw_ordinal
from zCalendar
order by dt
;

Open in new window

0
 
PortletPaulCommented:
details & sample data used
**MS SQL Server 2008 Schema Setup**:

    
    
    CREATE TABLE zCalendar
    	(  [dt] datetime
         , [isWorkday] int
         , [isHoliday] int
         , [Y] int
         , [FY] int
         , [Q] int
         , [M] int
         , [D] int
         , [DW] int
         
         , [dw_ordinal] int
    
         , [monthname] varchar(8)
         , [dayname] varchar(4)
         , [w] int)
    ;
    	
    INSERT INTO zCalendar
    	([dt], [isWorkday], [isHoliday], [Y], [FY], [Q], [M], [D], [DW], [monthname], [dayname], [w])
    VALUES
    	('2015-01-01 00:00:00', 1, 0, 2015, 2014, 4, 1, 1, 4, 'January', NULL, 1),
    	('2015-01-02 00:00:00', 1, 0, 2015, 2014, 4, 1, 2, 5, 'January', NULL, 1),
    	('2015-01-03 00:00:00', 0, 1, 2015, 2014, 4, 1, 3, 6, 'January', NULL, 1),
    	('2015-01-04 00:00:00', 0, 1, 2015, 2014, 4, 1, 4, 7, 'January', NULL, 2),
    	('2015-01-05 00:00:00', 1, 0, 2015, 2014, 4, 1, 5, 1, 'January', NULL, 2),
    	('2015-01-06 00:00:00', 1, 0, 2015, 2014, 4, 1, 6, 2, 'January', NULL, 2),
    	('2015-01-07 00:00:00', 1, 0, 2015, 2014, 4, 1, 7, 3, 'January', NULL, 2),
    	('2015-01-08 00:00:00', 1, 0, 2015, 2014, 4, 1, 8, 4, 'January', NULL, 2),
    	('2015-01-09 00:00:00', 1, 0, 2015, 2014, 4, 1, 9, 5, 'January', NULL, 2),
    	('2015-01-10 00:00:00', 0, 1, 2015, 2014, 4, 1, 10, 6, 'January', NULL, 2),
    	('2015-01-11 00:00:00', 0, 1, 2015, 2014, 4, 1, 11, 7, 'January', NULL, 3),
    	('2015-01-12 00:00:00', 1, 0, 2015, 2014, 4, 1, 12, 1, 'January', NULL, 3),
    	('2015-01-13 00:00:00', 1, 0, 2015, 2014, 4, 1, 13, 2, 'January', NULL, 3),
    	('2015-01-14 00:00:00', 1, 0, 2015, 2014, 4, 1, 14, 3, 'January', NULL, 3),
    	('2015-01-15 00:00:00', 1, 0, 2015, 2014, 4, 1, 15, 4, 'January', NULL, 3),
    	('2015-01-16 00:00:00', 1, 0, 2015, 2014, 4, 1, 16, 5, 'January', NULL, 3),
    	('2015-01-17 00:00:00', 0, 1, 2015, 2014, 4, 1, 17, 6, 'January', NULL, 3),
    	('2015-01-18 00:00:00', 0, 1, 2015, 2014, 4, 1, 18, 7, 'January', NULL, 4),
    	('2015-01-19 00:00:00', 1, 0, 2015, 2014, 4, 1, 19, 1, 'January', NULL, 4),
    	('2015-01-20 00:00:00', 1, 0, 2015, 2014, 4, 1, 20, 2, 'January', NULL, 4),
    	('2015-01-21 00:00:00', 1, 0, 2015, 2014, 4, 1, 21, 3, 'January', NULL, 4),
    	('2015-01-22 00:00:00', 1, 0, 2015, 2014, 4, 1, 22, 4, 'January', NULL, 4),
    	('2015-01-23 00:00:00', 1, 0, 2015, 2014, 4, 1, 23, 5, 'January', NULL, 4),
    	('2015-01-24 00:00:00', 0, 1, 2015, 2014, 4, 1, 24, 6, 'January', NULL, 4),
    	('2015-01-25 00:00:00', 0, 1, 2015, 2014, 4, 1, 25, 7, 'January', NULL, 5),
    	('2015-01-26 00:00:00', 1, 0, 2015, 2014, 4, 1, 26, 1, 'January', NULL, 5),
    	('2015-01-27 00:00:00', 1, 0, 2015, 2014, 4, 1, 27, 2, 'January', NULL, 5),
    	('2015-01-28 00:00:00', 1, 0, 2015, 2014, 4, 1, 28, 3, 'January', NULL, 5),
    	('2015-01-29 00:00:00', 1, 0, 2015, 2014, 4, 1, 29, 4, 'January', NULL, 5),
    	('2015-01-30 00:00:00', 1, 0, 2015, 2014, 4, 1, 30, 5, 'January', NULL, 5),
    	('2015-01-31 00:00:00', 0, 1, 2015, 2014, 4, 1, 31, 6, 'January', NULL, 5),
    	('2015-02-01 00:00:00', 0, 1, 2015, 2014, 4, 2, 1, 7, 'February', NULL, 6),
    	('2015-02-02 00:00:00', 1, 0, 2015, 2014, 4, 2, 2, 1, 'February', NULL, 6)
    ;

**Query 1**:

    update zCalendar
    set dw_ordinal = xtra.rn
    from zCalendar
    join (
      select dt, row_number() over(partition by y, m, dw order by dt) as rn
      from zCalendar
      ) xtra on zCalendar.dt = xtra.dt
    

**[Results][2]**:
    

**Query 2**:

    select
          dt, y, m, dw, dw_ordinal
    from zCalendar
    order by dt
    

**[Results][3]**:
    
    |                              DT |    Y | M | DW | DW_ORDINAL |
    |---------------------------------|------|---|----|------------|
    |  January, 01 2015 00:00:00+0000 | 2015 | 1 |  4 |          1 |
    |  January, 02 2015 00:00:00+0000 | 2015 | 1 |  5 |          1 |
    |  January, 03 2015 00:00:00+0000 | 2015 | 1 |  6 |          1 |
    |  January, 04 2015 00:00:00+0000 | 2015 | 1 |  7 |          1 |
    |  January, 05 2015 00:00:00+0000 | 2015 | 1 |  1 |          1 |
    |  January, 06 2015 00:00:00+0000 | 2015 | 1 |  2 |          1 |
    |  January, 07 2015 00:00:00+0000 | 2015 | 1 |  3 |          1 |
    |  January, 08 2015 00:00:00+0000 | 2015 | 1 |  4 |          2 |
    |  January, 09 2015 00:00:00+0000 | 2015 | 1 |  5 |          2 |
    |  January, 10 2015 00:00:00+0000 | 2015 | 1 |  6 |          2 |
    |  January, 11 2015 00:00:00+0000 | 2015 | 1 |  7 |          2 |
    |  January, 12 2015 00:00:00+0000 | 2015 | 1 |  1 |          2 |
    |  January, 13 2015 00:00:00+0000 | 2015 | 1 |  2 |          2 |
    |  January, 14 2015 00:00:00+0000 | 2015 | 1 |  3 |          2 |
    |  January, 15 2015 00:00:00+0000 | 2015 | 1 |  4 |          3 |
    |  January, 16 2015 00:00:00+0000 | 2015 | 1 |  5 |          3 |
    |  January, 17 2015 00:00:00+0000 | 2015 | 1 |  6 |          3 |
    |  January, 18 2015 00:00:00+0000 | 2015 | 1 |  7 |          3 |
    |  January, 19 2015 00:00:00+0000 | 2015 | 1 |  1 |          3 |
    |  January, 20 2015 00:00:00+0000 | 2015 | 1 |  2 |          3 |
    |  January, 21 2015 00:00:00+0000 | 2015 | 1 |  3 |          3 |
    |  January, 22 2015 00:00:00+0000 | 2015 | 1 |  4 |          4 |
    |  January, 23 2015 00:00:00+0000 | 2015 | 1 |  5 |          4 |
    |  January, 24 2015 00:00:00+0000 | 2015 | 1 |  6 |          4 |
    |  January, 25 2015 00:00:00+0000 | 2015 | 1 |  7 |          4 |
    |  January, 26 2015 00:00:00+0000 | 2015 | 1 |  1 |          4 |
    |  January, 27 2015 00:00:00+0000 | 2015 | 1 |  2 |          4 |
    |  January, 28 2015 00:00:00+0000 | 2015 | 1 |  3 |          4 |
    |  January, 29 2015 00:00:00+0000 | 2015 | 1 |  4 |          5 |
    |  January, 30 2015 00:00:00+0000 | 2015 | 1 |  5 |          5 |
    |  January, 31 2015 00:00:00+0000 | 2015 | 1 |  6 |          5 |
    | February, 01 2015 00:00:00+0000 | 2015 | 2 |  7 |          1 |
    | February, 02 2015 00:00:00+0000 | 2015 | 2 |  1 |          1 |



  [1]: http://sqlfiddle.com/#!3/35d2b/4

Open in new window

0
 
Andy GreenAuthor Commented:
Thanks, but I don't really want to manually add the ordinal field to 10 years worth of dates.

Can this be scripted for my current dataset?

Andy
0
 
PortletPaulCommented:
I see. Try it like this. Substitute "blah" with column name of your choice. & Change the data type of blah to suit.



alter table zCalendar add [blah] int
;

update zCalendar
set blah = xtra.rn
from zCalendar
join (
  select dt, row_number() over(partition by y, m, dw order by dt) as rn
  from zCalendar
  ) xtra on zCalendar.dt = xtra.dt
;

select
      dt, y, m, dw, blah
from zCalendar
order by dt
;
0
 
Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
>> I need 2 parameters, the day number (1-7) and its position in the month (1 First - 5 Last which could also be 4)

If you are looking for the second Tuesday of a week, then it would have to be between the 8th and the 14th.

The position on the month is merely:

Convert(int,(D+6)/7)
0
 
Andy GreenAuthor Commented:
Thanks Guys

I have used PortletPauls Solutions to add and populate the day ordinals. Thanks also to Phillip, your solution worked, but on this occasion I prefer the other option

Andy
0

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