Github user dongjoon-hyun commented on the issue:
https://github.com/apache/spark/pull/14397
Thank you for review, @hvanhovell .
For the recursive CTE queries, traditional DBMS supports optional
`RECURSIVE` keyword which computing **closures**, i.e., it iterates the
subquery until the result converge. For example, PostgreSQL, MSSQL, SQLite
supports `WITH RECURSIVE` syntax officially.
For the overlap of `ResolveRelations` rule, this rule calls
`lookupRelation` to check the name conflict between the base relations and
CTEs. As a side effect, it resolves the relations, too. Here is the reasons.
- To check the conflict, this is the only simplest way.
- For the performance, this patch only call one `lookupRelation` for
`UnresolvedRelation`.
- `ResolveRelations` rule do not try resolve again and will not
complain about that.
- The remaining general and exceptional rules like file-based datasource
should be in `ResolveRelations`. We can add more datasources there, not here.
For Hive, the recursive queries and `RECURSIVE` syntax are not supported.
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