[GitHub] [spark] dtenedor commented on a diff in pull request #42810: [SPARK-45075][SQL] Fix alter table with invalid default value will not report error

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

dtenedor commented on code in PR #42810:
URL: https://github.com/apache/spark/pull/42810#discussion_r1316137847


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/v2AlterTableCommands.scala:
##########
@@ -228,6 +228,15 @@ case class AlterColumn(
       TableChange.updateColumnPosition(colName, newPosition.position)
     }
     val defaultValueChange = setDefaultExpression.map { newDefaultExpression =>
+      if (newDefaultExpression.nonEmpty) {

Review Comment:
   The new default expression can't be an empty string because that will not parse as a SQL expression. Therefore it is acceptable to use the empty string as a sentinel value to indicate that no default value is associated with the target column.



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