Alternatives to Returning 0 If Value Is Null in postgreSQL/Redshift [Duplicate]

You could try using a case expression:

(case when sum(ScorePrem) = 0 then 0
      else sum(Score) / sum(ScorePrem)
 end)

However, your code should work.

EDIT:

You have at least one problem in the second query. You are using = to assign an alias. But in Redshift that is just a boolean expression -- and one not in the GROUP BY. So:

SELECT calendar_month_id, day_of_month, month_name, DaysRemaining, 
       'Entire' as RPTBRANCH, 1 as TotalGrp,
       sum(Score) as score,
       SUM(ScorePrem) as ScorePrem,
       coalesce(sum(Score)/nullif(sum(ScorePrem),0),0) as percent
FROM  #temp_score
GROUP BY calendar_month_id, day_of_month, month_name, DaysRemaining