Full YR calendar & row generators -probs with mnths that have 28/29/30 days

Question

Hello,
With Rod West's advice i've been able to build an absence calendar report using Row Generators, see the learndiscoverer blog (http://learndiscoverer.blogspot.com/2008/10/row-generators.html) for more details on row generators.
I have hit a problem with using dates as a data point (or the basis of a datapoint) in crosstabs.
I'm building a crosstab that needs to look at a years worth of absence for a person. Using 2 row generators, 1 producing 12 months (last day of each month as a date, formatted to fmMonth) down the side and the other with 31 rows running along the top for the days in that month.
The data point is a calculation that inserts the absence category on each day that a person is absent. This works brilliantly for one month. However the datapoint is a derivative of the month/year and the 31 days created by the row generator, which causes problems for certain months.
If, for example, I need to produce the report for January and February 2008 it will produce an error saying not a valid date for month. This is because there are 31 days running along the top and the datapoint is using 31 days in both Jan & Feb. As there were only 29 days during Feb in 2008 the error occurs when the datapoint creates 30-Feb-2008 & 31-Feb-2008.
I have tried to make the datapoint calculation return NULL for these dates but it won't allow it because the datapoint is must be some sort of date. I have tried to convert these erroneous dates to 01-Jan-1900 and then omit them from the report with a condition, i think this may be the solution, but i'm not getting anywhere with it.
If anyone knows a better way of doing this i'd be really grateful if you could let me know.
Also, just one other thing. Does anyone know how to format a date to a day in the format Mon, Tues, Wed etc. I can get the full day but need narrower columns.
Thanks,
Lloyd Thomas

Answer 1

Hi Rod,
This is brilliant! I'm sorry about the confusion I caused over the dates in the generator.
There is a problem here though. I've got to_date('01-JAN-'||:pyear)+n-1 along the top. Down the side of the cross tab I have LAST_DAY(TO_DATE('01-JAN-'||:pyear)+( Days in Year-1 )), formatted to FmMonth.
The data point is MAX(CASE WHEN "Dates in the Year" BETWEEN Date Start AND Absence Finish THEN Absence Category ELSE '' END).
The multiple absences over the year are causing duplicate rows. Once converted to a table i can see that each day of the year brings in duplicate rows for every absence a person has had. The MAX statement works in terms of identifying the correct row but I cannot get rid of the other rows. I can't do an IS NOT NULL condition because it will also remove days where people where not absent.
I think the problem with the LAST_DAY(TO_DATE('01-JAN-'||:pyear)+( Days in Year-1 )) calculation but i'm trying to make it return one month.
Any help appreciated.
Thanks,
Lloyd