Github user tanejagagan commented on a diff in the pull request:
https://github.com/apache/spark/pull/17174#discussion_r104481076
--- 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 --
Thanks for pointing that out.
After applying the PR ` '10' < current_timestamp` does return `null` and
its breaking the semantics.
The fix to this issue is very important. We have seen order of magnitude
performance difference if string is correctly casted to timestamp for Literals
in SQL and most of these SQLs are generated using some BI tool.
Any other suggestion to fix this issue? Shall i make it more restrictive so
that null cases are better covered. i.e
`if( expr.foldable && expressed.eval( null ) !=null )
cast to timestamp`
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