[IMPALA-4336] Wrong results with nested union operands due to missing casts.

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: Impala 2.3.0, Impala 2.5.0, Impala 2.4.0, Impala 2.6.0, Impala 2.7.0
• Fix Version/s: Impala 2.8.0
• Component/s: Frontend
• Labels: correctness
• Target Version: Impala 2.8.0
• Assignee: Alexander Behm
• Reporter: Alexander Behm
• Created: 21/Oct/16 20:49
• Updated: 15/Nov/16 13:05
• Resolved: 03/Nov/16 14:43

Description

Unions with nested unions can produce incorrect results due to missing casts.
This bug can happen for both UNION ALL and UNION DISTINCT.

Repro:

create table t (d double);
insert into t values(5.5);

select d from t union all values(cast(6.2 as float));
+------------------------+
| d                      |
+------------------------+
| 5.5                    |
| 5.369229582389968e-315 |
+------------------------+

select d from t union all (select 10 union all select 20);
+------------------------+
| d                      |
+------------------------+
| 5.5                    |
| 4.940656458412465e-323 |
| 9.881312916824931e-323 |
+------------------------+

The underlying problem is that after unnesting unions we need to re-apply casts to the exprs of the unnested operands which my not be the same as the exprs of the original operand.