This is definitely a bug. Thanks for the clear report and reproduction. It's not IMPALA-7957 but is somewhat related. This is new to us so I filed https://issues.apache.org/jira/browse/IMPALA-10182 to track it.   It looks like it can only happen when you have a UNION ALL, plus subqueries where the same column appears twice in the select list, plus NULL values in those  columns.   You can work around the issue by removing the duplicated entries in the subquery select list. E.g. the following query is equivalent and returns the expected results.   SELECT MIN(t_53.c_41) c_41, CAST(NULL AS DOUBLE) c_43, CAST(NULL AS BIGINT) c_44, t_53.c2 c2, t_53.c2 c3s0, t_53.c4 c4, t_53.c4 c5s0 FROM ( SELECT t.productsubcategorykey c_41, t.productline c2, t.productsubcategorykey c4 FROM as_adventure.t1 t WHERE true GROUP BY 2, 3 ) t_53 GROUP BY 4, 5, 6, 7 UNION ALL SELECT MIN(t_53.c_41) c_41, CAST(NULL AS DOUBLE) c_43, CAST(NULL AS BIGINT) c_44, t_53.c2 c2, t_53.c2 c3s0, t_53.c5s0 c4, t_53.c5s0 c5s0 FROM ( SELECT t.productsubcategorykey c_41, t.productline c2, t.productsubcategorykey c5s0 FROM as_adventure.t1 t WHERE true GROUP BY 2, 3) t_53 GROUP BY 4, 5, 6, 7;   ... View more