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_r321960243
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala
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@@ -526,6 +529,62 @@ trait CheckAnalysis extends PredicateHelper {
plan.setAnalyzed()
}
+ /**
+ * Recursion according to SQL standard comes with several limitations due to
the fact that only
+ * those operations are allowed where the new set of rows can be computed
from the result of the
+ * previous iteration. This implies that a recursive reference can't be used
in some kinds of
+ * joins and aggregations.
+ * A further constraint is that a recursive term can contain one recursive
reference only (except
+ * for using it on different sides of a UNION).
+ *
+ * This rules checks that these restrictions are not violated and returns
the original plan.
Review comment:
```suggestion
* This rule checks that these restrictions are not violated and returns
the original plan.
```
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