milanisvet commented on code in PR #49518:
URL: https://github.com/apache/spark/pull/49518#discussion_r1925279434


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveWithCTE.scala:
##########
@@ -183,4 +184,52 @@ object ResolveWithCTE extends Rule[LogicalPlan] {
         columnNames.map(UnresolvedSubqueryColumnAliases(_, ref)).getOrElse(ref)
     }
   }
+
+  /**
+   * Checks if data types of anchor and recursive terms of a recursive CTE 
definition match.
+   */
+  def checkDataTypesAnchorAndRecursiveTerm(unionLoop: UnionLoop): Unit = {
+    val anchorOutputDatatypes = unionLoop.anchor.output.map(_.dataType)
+    val recursiveTermOutputDatatypes = 
unionLoop.recursion.output.map(_.dataType)
+
+    if (!anchorOutputDatatypes.zip(recursiveTermOutputDatatypes).forall {
+      case (anchorDT, recursionDT) => DataType.equalsStructurally(anchorDT, 
recursionDT, true)

Review Comment:
   Rewritten, but I might completely remove data type checking as I realized 
that we might end up in some unexpected behavior.
   ``` 
   WITH RECURSIVE r(level, data) AS (
     VALUES (0, 0)
     UNION ALL
     SELECT level + 1, r.data
     FROM r
     WHERE r.level < 9
   )
   SELECT * FROM r
   ```
   This query will throw data type error although it should not.
   
   The queries for which data type error should indeed be thrown should end up 
anyway in `[CANNOT_MERGE_INCOMPATIBLE_DATA_TYPE]`.
   I will try with more examples to confirm this



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