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The following query is producing incorrect results: select t2.int_col y from alltypessmall t1 left outer join alltypestiny t2 on t1.int_col = t2.int_col group by 1 ... due to nulls not being aggregated properly on multiple nodes. This is because the value equivalency graph is being set for the join conjunct on an outer join. When a hash join partition node is being used, there is an optimization that skips the aggregation step that combines groups across nodes if, based on the value transfer graph, it deduces that all data for the partition column is being sent to the same node. The bug here is that even though an outer join is using an equi-conjunct, the left and right side are different when data is not found on the outer join side, where it becomes null. The fix is to avoid registering the equi-conjunct if the values are not always equal. Change-Id: I57e9d4ad4c4af5a4c268e43ac2937064dab6ffd7 Reviewed-on: http://gerrit.cloudera.org:8080/22138 Reviewed-by: Michael Smith <michael.smith@cloudera.com> Reviewed-by: Riza Suminto <riza.suminto@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Steve Carlin <scarlin@cloudera.com>