Github user viirya commented on a diff in the pull request: https://github.com/apache/spark/pull/17174#discussion_r105097503 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala --- @@ -324,14 +324,22 @@ object TypeCoercion { // We should cast all relative timestamp/date/string comparison into string comparisons // This behaves as a user would expect because timestamp strings sort lexicographically. // i.e. TimeStamp(2013-01-01 00:00 ...) < "2014" = true - case p @ BinaryComparison(left @ StringType(), right @ DateType()) => - p.makeCopy(Array(left, Cast(right, StringType))) - case p @ BinaryComparison(left @ DateType(), right @ StringType()) => - p.makeCopy(Array(Cast(left, StringType), right)) - case p @ BinaryComparison(left @ StringType(), right @ TimestampType()) => - p.makeCopy(Array(left, Cast(right, StringType))) - case p @ BinaryComparison(left @ TimestampType(), right @ StringType()) => - p.makeCopy(Array(Cast(left, StringType), right)) + // If StringType is foldable then we need to cast String to Date or Timestamp type + // which would give order of magnitude performance gain as well as preserve the behavior + // achieved by expressed above + // TimeStamp(2013-01-01 00:00 ...) < Cast( "2014" as timestamp) = true + case p @ BinaryComparison(left @ StringType(), right) if dateOrTimestampType(right) => + if (left.foldable) { + p.makeCopy(Array(Cast(left, right.dataType), right)) --- End diff -- Without this change, I think you can still explicitly cast the string to time/date in order to speed up the comparison, right?
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