[IMPALA-6518] Fix the output type of a decimal union for decimal_v2

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 3.0
• Fix Version/s: Impala 3.0, Impala 2.13.0
• Component/s: Frontend
• Epic Color: ghx-label-9
• Assignee: Taras Bobrovytsky
• Reporter: Taras Bobrovytsky
• Created: 13/Feb/18 22:38
• Updated: 18/Jul/18 15:00
• Resolved: 30/Apr/18 19:24

Description

In the following query, the type of c1 is decimal(38, 38) for both decimal v1 and v2.

select c1 from (
select cast(1 as decimal(38, 0)) as c1
union all
select cast(0.1 as decimal(38, 38)) as c1) t

This means that we are truncating from the front. It would make more sense to truncate from the back and round when decimal v2 is enabled. The output type should be (38, 6). This is what we do for other mathematical operations, such as addition.

Issue Links

• breaks: IMPALA-7211 Query with a decimal between predicate needlessly fails