So there is a problem that I cannot see how to resolve.  I've worked out most of the elements that I need to do the Churn Rate calculation but there is an error.  Here is the code
 

-- Get the current and previous Qtr Subscriptions
q = load "Beattie_Subs";
Subs = group q by (Subscription_Date_Year, Subscription_Date_Quarter);
Subs = foreach Subs generate Subscription_Date_Year, Subscription_Date_Quarter, count() as CurrQtrSubs, sum(count()) over([-1 .. -1] partition by all order by Subscription_Date_Year) as PrevQtrSubs;

-- Fill the Subs gaps
Subs = fill Subs by (dateCols=(Subscription_Date_Year, Subscription_Date_Quarter, "Y-Q"));

-- Get the current and previous Qtr Cancellations
q = load "Beattie_Subs";
Canc = group q by (Churn_Date_Year, Churn_Date_Quarter);
Canc = foreach Canc generate Churn_Date_Year, Churn_Date_Quarter, count() as CurrQtrCanc, sum(count()) over([-1 .. -1] partition by all order by Churn_Date_Year) as PrevQtrCanc;

-- Fill the Canc gaps
Canc = fill Canc by (dateCols=(Churn_Date_Year, Churn_Date_Quarter, "Y-Q"));

-- Combine them
result = cogroup Subs by ('Subscription_Date_Year', 'Subscription_Date_Quarter') full, Canc by ('Churn_Date_Year', 'Churn_Date_Quarter');

-- Calc churn (to be completed)
result = foreach result generate Subs['Subscription_Date_Year'] as XX, Subs['Subscription_Date_Quarter'] as YY, 
coalesce(sum(Subs[CurrQtrSubs]),0) as 'CurrQtrSubs', 
coalesce(sum(Subs[PrevQtrSubs]),0) as 'PrevQtrSubs', 
coalesce(sum(Canc[CurrQtrCanc]),0) as 'CurrQtrCanc', 
coalesce(sum(Canc[PrevQtrCanc]),0) as 'PrevQtrCanc';

The reasons I can't complete is a problem with the Fill command.  When this is run you get a table that looks like this.  The Previous Quarter is being brought down to the Current Quarter fine.  But where an extra Quarter has been brought in by the Fill it is being skipped.



SAQL is not well documented and there are few examples.  How should I structure the logic to work?