add config flag for recursive ctes

Author: matthewgapp

datafusion/common/src/config.rs

@@ -278,6 +278,11 @@ config_namespace! {
         /// Hive. Note that this setting does not affect reading partitioned
         /// tables (e.g. `/table/year=2021/month=01/data.parquet`).
         pub listing_table_ignore_subdirectory: bool, default = true
+
+        /// Should DataFusion support recursive CTEs
+        /// Defaults to false since this feature is a work in progress and may not
+        /// behave as expected
+        pub enable_recursive_ctes: bool, default = false
     }
 }
 

datafusion/sql/src/query.rs

@@ -54,7 +54,18 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
             // Process CTEs from top to bottom
             // do not allow self-references
             if with.recursive {
-                return not_impl_err!("Recursive CTEs are not supported");
+                if self
+                    .context_provider
+                    .options()
+                    .execution
+                    .enable_recursive_ctes
+                {
+                    return plan_err!(
+                        "Recursive CTEs are enabled but are not yet supported"
+                    );
+                } else {
+                    return not_impl_err!("Recursive CTEs are not supported");
+                }
             }
 
             for cte in with.cte_tables {