Re: [PR] [SPARK-50707][SQL] Enable casting to/from char/varchar [spark]

["mihailom-db (via GitHub)" <gi...@apache.org>]

mihailom-db commented on code in PR #49340:
URL: https://github.com/apache/spark/pull/49340#discussion_r1901853840


##########
sql/api/src/main/scala/org/apache/spark/sql/types/StringType.scala:
##########
@@ -129,6 +130,60 @@ case object StringType
 
 sealed trait StringConstraint
 
+case object StringHelper extends PartialOrdering[StringConstraint] {
+  override def tryCompare(x: StringConstraint, y: StringConstraint): Option[Int] = {
+    (x, y) match {
+      case (NoConstraint, NoConstraint) => Some(0)
+      case (NoConstraint, _) => Some(-1)
+      case (_, NoConstraint) => Some(1)
+      case (FixedLength(l1), FixedLength(l2)) => Some(l2.compareTo(l1))
+      case (FixedLength(l1), MaxLength(l2)) if l1 <= l2 => Some(1)
+      case (MaxLength(l1), FixedLength(l2)) if l1 >= l2 => Some(-1)
+      case (MaxLength(l1), MaxLength(l2)) => Some(l2.compareTo(l1))
+      case _ => None
+    }
+  }
+
+  override def lteq(x: StringConstraint, y: StringConstraint): Boolean = {
+    tryCompare(x, y).exists(_ <= 0)
+  }
+
+  override def gteq(x: StringConstraint, y: StringConstraint): Boolean = {
+    tryCompare(x, y).exists(_ >= 0)
+  }
+
+  override def equiv(x: StringConstraint, y: StringConstraint): Boolean = {
+    tryCompare(x, y).contains(0)
+  }
+
+  def isPlainString(s: StringType): Boolean = equiv(s.constraint, NoConstraint)
+
+  def isMoreConstrained(a: StringType, b: StringType): Boolean =
+    gteq(a.constraint, b.constraint)
+
+  def tightestCommonString(s1: StringType, s2: StringType): Option[StringType] = {
+    if (s1.collationId != s2.collationId) {
+      return None
+    }
+    if (!SqlApiConf.get.preserveCharVarcharTypeInfo) {
+      return Some(StringType(s1.collationId))

Review Comment:
   Why not just return s2 as previous behaviour here?



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