set analysis for null value

[#1]

Hi, I have a question about Set Analysis.

I want to calculate the number of first-time mom and non-first-time mom, the conditions are

1. First time mom : First born flag = Y and only has one due date

2. Non-first time mom : First born flag <> Y or has more than one due date

For first time mom, I wrote

=count({$Customer_First_Born_Flag ={Y}, Customer_Due_Date1={ }, Customer_Due_Date2= { }>} distinct Customer_Key), which didn't work.

But =count({$Customer_First_Born_Flag ={Y}>} distinct Customer_Key) worked!!

Why is that? Isn't { } represents null value? Please help please!!

[#2]

I tried to do this, this didn't work either:

=

count({$<Customer_First_Born_Flag = {Y}, Customer_Due_Date1 = {*}>

-$<

Customer_First_Born_Flag = {Y}, Customer_Due_Date1 = {*},Customer_Due_Date2 = {*}>

-$<

Customer_First_Born_Flag = {Y}, Customer_Due_Date1 = {*},Customer_Due_Date2 = {*}, Customer_Due_Date3= {*}>

-$<

Customer_First_Born_Flag = {Y}, Customer_Due_Date1 = {*},Customer_Due_Date2 = {*}, Customer_Due_Date3 = {*}, Customer_Due_Date4 = {*}>

-$<

Customer_First_Born_Flag = {Y}, Customer_Due_Date1 = {*},Customer_Due_Date2 = {*}, Customer_Due_Date3 = {*}, Customer_Due_Date4 = {*}, Customer_Due_Date5= {*}>

-$<Customer_First_Born_Flag = {Y}, Customer_Due_Date1 = {*},Customer_Due_Date2 = {*}, Customer_Due_Date3 = {*}, Customer_Due_Date4 = {*}, Customer_Due_Date5 = {*}, Customer_Due_Date6= {*}>

}

distinct Customer_Key)

[#3]

Hello,

I'm just wondering do the due dates really matter because you're flagging the first time moms with "Y" already.

First time moms:

=count ( distinct { $<Customer_First_Born_Flag = {"Y"} >} Customer_Key)

Non-First timers:

=count ( distinct { $<Customer_First_Born_Flag -= {"Y"} >} Customer_Key)

Do you need to count how many kids they have for the non first time moms? Then you will need to take the due dates into account.