[jira] [Created] (IMPALA-6660) -0/+0 floating point do not compare as equal in hash table

["Tim Armstrong (JIRA)" <ji...@apache.org>]

Tim Armstrong created IMPALA-6660:
-------------------------------------

             Summary: -0/+0 floating point do not compare as equal in hash table
                 Key: IMPALA-6660
                 URL: https://issues.apache.org/jira/browse/IMPALA-6660
             Project: IMPALA
          Issue Type: Bug
          Components: Backend
    Affects Versions: Impala 2.11.0, Impala 2.10.0, Impala 2.9.0, Impala 2.8.0, Impala 2.7.0, Impala 2.6.0, Impala 2.12.0
            Reporter: Tim Armstrong


This can happen because we hash the binary representation of the numbers. -0/0 should be treated as equal.
{noformat}
[localhost:21000] > select * from (select cast("-0" as float) c1) v1,  (select cast("0" as float) c2) v2 where v1.c1 = v2.c2;
Fetched 0 row(s) in 0.12s
[localhost:21000] > select * from (select cast("0" as float) c1) v1,  (select cast("0" as float) c2) v2 where v1.c1 = v2.c2;
+----+----+
| c1 | c2 |
+----+----+
| 0  | 0  |
+----+----+
Fetched 1 row(s) in 0.11s
[localhost:21000] > select * from (select cast("-0" as float) c1) v1,  (select cast("-0" as float) c2) v2 where v1.c1 = v2.c2;
+----+----+
| c1 | c2 |
+----+----+
| -0 | -0 |
+----+----+
Fetched 1 row(s) in 0.11s
{noformat}

With aggregations, we get separate groups. I could see the argument either way on whether this is the correct behaviour for group by. The behaviour here is tied to the behaviour in the join right now, so we should make sure to add a test for this case when fixing the join.
{noformat}
[localhost:21000] > select distinct * from (values(cast("-0" as float)), (cast("0" as float))) v;
+---------------------+
| cast('-0' as float) |
+---------------------+
| -0                  |
| 0                   |
+---------------------+
{noformat}




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