Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/23197#discussion_r238110847
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -119,14 +121,26 @@ object TypeCoercion {
* other is a Timestamp by making the target type to be String.
*/
private def findCommonTypeForBinaryComparison(
- dt1: DataType, dt2: DataType, conf: SQLConf): Option[DataType] =
(dt1, dt2) match {
- // 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
+ left: Expression,
+ right: Expression,
+ conf: SQLConf): Option[DataType] = (left.dataType, right.dataType)
match {
+ // We should cast all relative timestamp/date/string comparison into
string comparisons only if
+ // the particular literal value cannot been converted into a valid
Timestamp/Date. If the value
+ // can be converted into a valid TimeStamp/Date then we cast the right
side literal value to
+ // 'Timestamp'/'Date', for more details refer the description provided
in stringToTimestamp()
+ // method.
--- End diff --
We will not change the existing Type Coercion rules in the current stage.
We plan to re-visit the whole type coercion rules by following some other
systems, e.g., PostgreSQL
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