[GitHub] [druid] LakshSingla commented on a change in pull request #12017: Fix the error case when there are multi top level unions

[GitBox <gi...@apache.org>]

LakshSingla commented on a change in pull request #12017:
URL: https://github.com/apache/druid/pull/12017#discussion_r761075609



##########
File path: sql/src/main/java/org/apache/druid/sql/calcite/planner/DruidPlanner.java
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@@ -431,25 +431,26 @@ private PlannerResult planExplanation(
    */
   private String explainSqlPlanAsNativeQueries(DruidRel<?> rel) throws JsonProcessingException
   {
-    // Only if rel is an instance of DruidUnionRel, do we run multiple native queries corresponding to single SQL query
-    // Also, DruidUnionRel can only be a top level node, so we don't need to check for this condition in the subsequent
-    // child nodes
     ObjectMapper jsonMapper = plannerContext.getJsonMapper();
     List<DruidQuery> druidQueryList;
-    if (rel instanceof DruidUnionRel) {
-      druidQueryList = rel.getInputs().stream().map(childRel -> (DruidRel<?>) childRel).map(childRel -> {
-        if (childRel instanceof DruidUnionRel) {
-          log.error("DruidUnionRel can only be the outermost RelNode. This error shouldn't be encountered");
-          throw new ISE("DruidUnionRel is only supported at the outermost RelNode.");
-        }
-        return childRel.toDruidQuery(false);
-      }).collect(Collectors.toList());
-    } else {
-      druidQueryList = ImmutableList.of(rel.toDruidQuery(false));
+    try {
+      druidQueryList = flattenOutermostRel(rel)
+          .stream()
+          .map(druidRel -> druidRel.toDruidQuery(false))
+          .collect(Collectors.toList());
+
+    }
+    catch (UnsupportedOperationException unsupportedOperationException) {

Review comment:
       `DruidUnionRel` throws it for unsupported operations: `https://github.com/apache/druid/blob/1f95a42bb8b32c314934e8e2ecdeb6569c7e8db3/sql/src/main/java/org/apache/druid/sql/calcite/rel/DruidUnionRel.java#L125` (Those operations which can be done on queries which translate directly to native queries). Here `toDruidQuery` can throw the exception.




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