[GitHub] drill pull request #889: DRILL-5691: enhance scalar sub queries checking for...

[amansinha100 <gi...@git.apache.org>]

Github user amansinha100 commented on a diff in the pull request:

    https://github.com/apache/drill/pull/889#discussion_r137295692
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/join/JoinUtils.java ---
    @@ -203,35 +203,27 @@ public static void addLeastRestrictiveCasts(LogicalExpression[] leftExpressions,
       }
     
       /**
    -   * Utility method to check if a subquery (represented by its root RelNode) is provably scalar. Currently
    -   * only aggregates with no group-by are considered scalar. In the future, this method should be generalized
    -   * to include more cases and reconciled with Calcite's notion of scalar.
    +   * Utility method to check if a subquery (represented by its root RelNode) is provably scalar.
        * @param root The root RelNode to be examined
        * @return True if the root rel or its descendant is scalar, False otherwise
        */
       public static boolean isScalarSubquery(RelNode root) {
    -    DrillAggregateRel agg = null;
    -    RelNode currentrel = root;
    -    while (agg == null && currentrel != null) {
    -      if (currentrel instanceof DrillAggregateRel) {
    -        agg = (DrillAggregateRel)currentrel;
    -      } else if (currentrel instanceof RelSubset) {
    -        currentrel = ((RelSubset)currentrel).getBest() ;
    -      } else if (currentrel.getInputs().size() == 1) {
    -        // If the rel is not an aggregate or RelSubset, but is a single-input rel (could be Project,
    -        // Filter, Sort etc.), check its input
    -        currentrel = currentrel.getInput(0);
    -      } else {
    -        break;
    -      }
    -    }
    -
    -    if (agg != null) {
    -      if (agg.getGroupSet().isEmpty()) {
    -        return true;
    +    RelMetadataQuery relMetadataQuery = RelMetadataQuery.instance();
    +    RelNode currentRel = root;
    +    for (; ; ) {
    --- End diff --
    
    If the currentRel happens to be null we should not enter the loop.  Better to keep the while(currentRel != null) and have the return FALSE at the end. 


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