[GitHub] [spark] srowen commented on a diff in pull request #39843: [SPARK-39347] [SS] Bug fix for time window calculation when event time < 0

["srowen (via GitHub)" <gi...@apache.org>]

srowen commented on code in PR #39843:
URL: https://github.com/apache/spark/pull/39843#discussion_r1094623314


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveTimeWindows.scala:
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@@ -103,9 +115,10 @@ object TimeWindowing extends Rule[LogicalPlan] {
 
         def getWindow(i: Int, dataType: DataType): Expression = {
           val timestamp = PreciseTimestampConversion(window.timeColumn, dataType, LongType)
-          val lastStart = timestamp - (timestamp - window.startTime
-            + window.slideDuration) % window.slideDuration
-          val windowStart = lastStart - i * window.slideDuration
+          val lastStart = timestamp - (timestamp - window.startTime) % window.slideDuration

Review Comment:
   This seems a little complicated, and need not involve CaseWhen. You just always want to subtract a nonnegative amount here.
   
   ```
   val remainder = (timestamp - window.startTime) % window.slideDuration
   val lastStart = timestamp - (if (remainder < 0) remainder + window.slideDuration else remainder)
   ```



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