[vb.net] Find first and last day for previous calendar month in SQL Server Reporting Services (VB.Net)

I'm creating a report in MS SQL Server Reporting Services and need to set the default Start and End Date report parameters to be the first and last dates of the previous calendar month and need help.

The report is generated on the 2nd calendar day of the month and I need values for:

Previous Calendar Month
- first day
- last day

I've been working with DateAdd, but have not been successful at creating an Expression (in VB.NET as I understand it). I would really appreciate any help you can give me!

I was looking for a simple answer to solve this myself. here is what I found

This will split the year and month, take one month off and get the first day.

firstDayInPreviousMonth = DateSerial(Year(dtmDate), Month(dtmDate) - 1, 1)

Gets the first day of the previous month from the current

lastDayInPreviousMonth = DateSerial(Year(dtmDate), Month(dtmDate), 0)

More details can be found at: http://msdn.microsoft.com/en-us/library/aa227522%28v=vs.60%29.aspx

Randall, here are the VB expressions I found to work in SSRS to obtain the first and last days of any month, using the current month as a reference:

First day of last month:

=dateadd("m",-1,dateserial(year(Today),month(Today),1)) 

First day of this month:

=dateadd("m",0,dateserial(year(Today),month(Today),1)) 

First day of next month:

=dateadd("m",1,dateserial(year(Today),month(Today),1)) 

Last day of last month:

=dateadd("m",0,dateserial(year(Today),month(Today),0))

Last day of this month:

=dateadd("m",1,dateserial(year(Today),month(Today),0))

Last day of next month:

=dateadd("m",2,dateserial(year(Today),month(Today),0))

The MSDN documentation for the VisualBasic DateSerial(year,month,day) function explains that the function accepts values outside the expected range for the year, month, and day parameters. This allows you to specify useful date-relative values. For instance, a value of 0 for Day means "the last day of the preceding month". It makes sense: that's the day before day 1 of the current month.

in C#:

new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).AddMonths(-1)
new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).AddDays(-1)

        Dim aDate As DateTime = #3/1/2008# 'sample date
    Dim StartDate As DateTime = aDate.AddMonths(-1).AddDays(-(aDate.Day - 1))
    Dim EndDate As DateTime = StartDate.AddDays(DateTime.DaysInMonth(StartDate.Year, StartDate.Month) - 1)

    'to access just the date portion
    ' StartDate.Date
    ' EndDate.Date

These functions have been very helpful to me - especially in setting up subscription reports; however, I noticed when using the Last Day of Current Month function posted above, it works as long as the proceeding month has the same number of days as the current month. I have worked through and tested these modifications and hope they help other developers in the future:

Date Formulas: Find the First Day of Previous Month:

DateAdd("m", -1, DateSerial(Year(Today()), Month(Today()), 1))

Find Last Day of Previous Month:

DateSerial(Year(Today()), Month(Today()), 0)

Find First Day of Current Month:

DateSerial(Year(Today()),Month(Today()),1)

Find Last Day of Current Month:

DateSerial(Year(Today()),Month(DateAdd("m", 1, Today())),0)

I was having some difficulty translating actual VB.NET to the Expression subset that SSRS uses. You definitely inspired me though and this is what I came up with.

StartDate  
=dateadd("d",0,dateserial(year(dateadd("d",-1,dateserial(year(Today),month(Today),1))),month(dateadd("d",-1,dateserial(year(Today),month(Today),1))),1))

End Date
=dateadd("d",0,dateserial(year(Today),month(Today),1))  

I know it's a bit recursive for the StartDate (first day of last month). Is there anything I'm missing here? These are strictly date fields (i.e. no time), but I think this should capture leap year, etc.

How did I do?

I'm not familiar with SSRS, but you can get the beginning and end of the previous month in VB.Net using the DateTime constructor, like this:

Dim prevMonth As DateTime = yourDate.AddMonths(-1)

Dim prevMonthStart As New DateTime(prevMonth.Year, prevMonth.Month, 1)
Dim prevMonthEnd As New DateTime(prevMonth.Year, prevMonth.Month, DateTime.DaysInMonth(prevMonth.Year, prevMonth.Month))

(yourDate can be any DateTime object, such as DateTime.Today or #12/23/2003#)

Dim thisMonth As New DateTime(DateTime.Today.Year, DateTime.Today.Month, 1)
Dim firstDayLastMonth As DateTime
Dim lastDayLastMonth As DateTime

firstDayLastMonth = thisMonth.AddMonths(-1)
lastDayLastMonth = thisMonth.AddDays(-1)

This one will give you date no time:

=FormatDateTime(DateAdd("m", -1, DateSerial(Year(Today()), Month(Today()), 1)), 
DateFormat.ShortDate)

This one will give you datetime:

=dateadd("m",-1,dateserial(year(Today),month(Today),1))