gianm commented on code in PR #16326:
URL: https://github.com/apache/druid/pull/16326#discussion_r1941496159
##########
extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/querykit/groupby/GroupByPostShuffleFrameProcessor.java:
##########
@@ -263,6 +267,41 @@ private void writeCurrentFrameIfNeeded() throws IOException
outputChannel.write(new FrameWithPartition(frame,
FrameWithPartition.NO_PARTITION));
frameWriter.close();
frameWriter = null;
+ outputRows += frame.numRows();
+ }
+ }
+
+ /**
+ * Generate a frame containing a single row with default values of all
aggregations if needed. This method uses
+ * {@link GroupingEngine#summaryRowPreconditions(GroupByQuery)} to determine
if such an operation is needed.
+ *
+ * Note that in cases where {@link
GroupingEngine#summaryRowPreconditions(GroupByQuery)} returns true, the
+ * preceding {@link GroupByPreShuffleFrameProcessorFactory} stage would use
an empty {@link ClusterBy}. Therefore,
+ * there would only be a single output partition of the prior stage, and
therefore a single instance of
+ * this processor. This ensures that only a single null-aggregations row is
generated for the entire stage.
+ */
+ private void writeEmptyAggregationsFrameIfNeeded() throws IOException
+ {
+ // Check isIncludeNullResultRow, which is populated by the SQL planner
when doing a query like GROUP BY ().
Review Comment:
Ah, this was an outdated comment. I removed it.
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