Debug calculation formula to avoid infinity when log(0) is encountered

models/marts/reporting/rep_exchange__survival_analysis.sql

@@ -107,7 +107,6 @@ compute_censored_subjects AS (
 
 ),
 
-
 compute_probability AS (
 
     SELECT
@@ -115,15 +114,25 @@ compute_probability AS (
 
         -- The survival probability represents the probability of customers that will not churn up to a specific tenure
         -- Example: survival_day = 61, survival_prob = 95%. For customers with 61 days of tenure, the customer has a 95% chance of not churning.
-        EXP(SUM(LN(1 - events / at_risk)) OVER (
+        -- When events / at_risk = 1, we replace value 1 with a value very near to 1, to prevent log 0 which causes infinity value
+        EXP(SUM(LN
+                (
+                CASE WHEN (1 - events / at_risk) = 0 THEN 0.999999 ELSE (1 - events / at_risk) END
+                )) 
+            OVER (
                 ORDER BY survival_time_days ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
                 ))      AS survival_probability,
 
-        100 * (1 - EXP(SUM(LN(1 - events / at_risk)) OVER (
+        100 * (1 - EXP(SUM(LN
+                (
+                CASE WHEN (1 - events / at_risk) = 0 THEN 0.999999 ELSE (1 - events / at_risk) END
+                )) 
+            OVER (
                 ORDER BY survival_time_days ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
                 )))     AS conversion_percentage,
 
-        SUM(events / at_risk) OVER (
+        SUM(events / at_risk) 
+            OVER (
             ORDER BY survival_time_days ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
                  )      AS cumulative_hazard,