kgyrtkirk commented on a change in pull request #1439:
URL: https://github.com/apache/hive/pull/1439#discussion_r482090289
##########
File path:
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveAggregateJoinTransposeRule.java
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@@ -303,6 +305,90 @@ public void onMatch(RelOptRuleCall call) {
}
}
+ /**
+ * Determines weather the give grouping is unique.
+ *
+ * Consider a join which might produce non-unique rows; but later the
results are aggregated again.
+ * This method determines if there are sufficient columns in the grouping
which have been present previously as unique column(s).
+ */
+ private boolean isGroupingUnique(RelNode input, ImmutableBitSet groups) {
+ if (groups.isEmpty()) {
+ return false;
+ }
+ RelMetadataQuery mq = input.getCluster().getMetadataQuery();
+ Set<ImmutableBitSet> uKeys = mq.getUniqueKeys(input);
+ for (ImmutableBitSet u : uKeys) {
+ if (groups.contains(u)) {
+ return true;
+ }
+ }
+ if (input instanceof Join) {
+ Join join = (Join) input;
+ RexBuilder rexBuilder = input.getCluster().getRexBuilder();
+ SimpleConditionInfo cond = new SimpleConditionInfo(join.getCondition(),
rexBuilder);
+
+ if (cond.valid) {
+ ImmutableBitSet newGroup =
groups.intersect(ImmutableBitSet.fromBitSet(cond.fields));
+ RelNode l = join.getLeft();
+ RelNode r = join.getRight();
+
+ int joinFieldCount = join.getRowType().getFieldCount();
+ int lFieldCount = l.getRowType().getFieldCount();
+
+ ImmutableBitSet groupL = newGroup.get(0, lFieldCount);
+ ImmutableBitSet groupR = newGroup.get(lFieldCount,
joinFieldCount).shift(-lFieldCount);
+
+ if (isGroupingUnique(l, groupL)) {
Review comment:
this method does a bit different thing - honestly I feeled like I'm in
trouble when I've given this name to it :)
this method checks if the given columns contain an unique column somewhere
in the covered joins; (this still sound fuzzy) so let's take an example
consider:
```
select c_id, sum(i_prize) from customer c join item i on(i.c_id=c.c_id)
```
* do an aggregate grouping by the column C_ID ; and sum up something
* below is a join which joins by C_ID
* asking wether C_ID is a unique column on top of the join is false; but
there is subtree in which C_ID is unique => so if we push the aggregate on that
branch the aggregation will be a no-op
I think this case is not handled by `areColumnsUnique`
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