[GitHub] [druid] abhishekagarwal87 commented on a change in pull request #11908: Improve the output of SQL explain message

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

abhishekagarwal87 commented on a change in pull request #11908:
URL: https://github.com/apache/druid/pull/11908#discussion_r752253808



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File path: sql/src/main/java/org/apache/druid/sql/calcite/planner/DruidPlanner.java
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@@ -384,6 +399,46 @@ private PlannerResult planExplanation(
     return new PlannerResult(resultsSupplier, getExplainStructType(rel.getCluster().getTypeFactory()));
   }
 
+  /**
+   * This method doesn't utilize the Calcite's internal {@link RelOptUtil#dumpPlan} since that tends to be verbose
+   * and not indicative of the native Druid Queries which will get executed
+   * This method assumes that the Planner has converted the RelNodes to DruidRels, and thereby we can implictly cast it
+   *
+   * @param rel Instance of the root {@link DruidRel} which is formed by running the planner transformations on it
+   * @return A string representing an array of native queries that correspond to the given SQL query, in JSON format
+   * @throws JsonProcessingException
+   */
+  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
+    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");
+          // TODO: Throw an error here

Review comment:
       should you throw an error here? 




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