Qlikview 11 for developers - Understanding while loop and master calendar

[#1]

This is from page 295. I don't understand how the looping works to generate temp_date. I know what is happening in the end - I get a calendar with all dates between two ranges. But, I don't understand how the steps are executed logically by Qlikview. Can someone please explain the logic in the  while load, step by step ?

[Master Calendar]:

LOAD DISTINCT
Year(Temp_Date) * 100 + Month(Temp_Date) as [Period]....etc.
;

LOAD DISTINCT
MonthStart($(vMinDate) + IterNo() - 1) as Temp_Date
AUTOGENERATE (1)
WHILE $(vMinDate) + IterNo() - 1 <= $(vMaxDate);

If this was a regular programming language, I'd do it like this -

int vMinDate = 1234;

int vMaxDate = 6789;

while(vMinDate < vMaxDate)

{

  Add a row which is equal to vMinDate in a Field;

  vMinDate = vMinDate + 1;

}

[swuehl]

The While loop is generating 1 record as long as the condition is true.

The important thing to know is that Iterno() returns the current iteration, i.e. 1 for the first execution, 2 for the second etc.

[#3]

Thanks. Can you also tell me how qlikview executes it, step by step ? The programming code which I gave is so simple and self-explanatory. But, the qlikview script is not.

[swuehl]

The programming code is probably simple and self-explanatory because you know the syntax.

To understand the QV script, you need to know some of the QV basics, e.g. input table / output table of a LOAD statement. Do you know the difference?

Maybe it's easier if you are trying to describe how you interprete the code, instead me more or less repeating something that's probably already written in the book.

[#5 · Accepted solution]

I read the manual and figured it out. Only one minor question remains. Why generate from month start instead of actual min date ?

LOAD DISTINCT
MonthStart($(vMinDate) + IterNo() - 1) as Temp_Date
AUTOGENERATE (1)
WHILE $(vMinDate) + IterNo() - 1 <= $(vMaxDate);

Preparation -

IterNo() = 0, since we have not started iterating yet.

Let the date for current iteration be currDate.

currDate =  $(vMinDate) + IterNo() - 1 = 1 + 0 - 1 = 0

vMinDate = 4/24/2014 (say. day 1)

vMaxDate = 4/30/2014 (say. day 7)

Steps -

1. Create column Temp_Date in memory.

2. IterNo() = IterNo() + 1

3. currDate = 1 + 1 - 1 = 1 (I.e day 1) 

4. add currDate as row to Temp_Date using AUTOGENERATE (1).

5. Repeat steps 2 to 4 while currDate <= vMaxDate

[swuehl]

That's a good question, I would also create the master calendar a little different. But without reading the part of the book, I don't know what the author intended. I agree it looks a bit complicated and creates more records first then needed at the end.