mgaido91 commented on a change in pull request #23531: [SPARK-24497][SQL]
Support recursive SQL query
URL: https://github.com/apache/spark/pull/23531#discussion_r321960168
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CTESubstitution.scala
##########
@@ -120,6 +125,124 @@ object CTESubstitution extends Rule[LogicalPlan] {
}
}
+ /**
+ * If recursion is allowed recursion handling starts with inserting
unresolved self-references
+ * ([[UnresolvedRecursiveReference]]) to places where a reference to the CTE
definition itself is
+ * found.
+ * If there is a self-reference then we need to check if structure of the
query satisfies the SQL
+ * recursion rules and insert the appropriate [[RecursiveRelation]] finally.
+ */
+ private def handleRecursion(
+ ctePlan: => LogicalPlan,
+ cteName: String,
+ allowRecursion: Boolean) = {
+ if (allowRecursion) {
+ // check if there is any reference to the CTE and if there is then treat
the CTE as recursive
+ val (recursiveReferencesPlan, recursiveReferenceCount) =
+ insertRecursiveReferences(ctePlan, cteName)
+ if (recursiveReferenceCount > 0) {
+ // if there is a reference then the CTE needs to follow one of these
structures
+ recursiveReferencesPlan match {
+ case SubqueryAlias(_, u: Union) =>
+ insertRecursiveRelation(cteName, Seq.empty, false, u)
+ case SubqueryAlias(_, Distinct(u: Union)) =>
+ insertRecursiveRelation(cteName, Seq.empty, true, u)
+ case SubqueryAlias(_, UnresolvedSubqueryColumnAliases(columnNames,
u: Union)) =>
+ insertRecursiveRelation(cteName, columnNames, false, u)
+ case SubqueryAlias(_, UnresolvedSubqueryColumnAliases(columnNames,
Distinct(u: Union))) =>
+ insertRecursiveRelation(cteName, columnNames, true, u)
+ case _ =>
+ throw new AnalysisException(s"Recursive query ${cteName} should
contain UNION or " +
+ s"UNION ALL statements only. This error can also be caused by
ORDER BY or LIMIT " +
+ s"keywords used on result of UNION or UNION ALL.")
Review comment:
```suggestion
"keywords used on result of UNION or UNION ALL.")
```
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