[IMPALA-11202] Round functions return types for decimals(X, 0) increase precision by 1

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Frontend
• Epic Color: ghx-label-7
• Assignee: Unassigned
• Reporter: Csaba Ringhofer
• Created: 25/Mar/22 14:16
• Updated: 25/Mar/22 14:16

Description

select typeof(ceil(cast(1 as decimal(1, 0))));
result: DECIMAL(2,0)

select typeof(ceil(cast(1 as decimal(38, 0))));
ERROR: AnalysisException: No matching function with signature: typeof(INVALID_TYPE).

Meanwhile precision is not increased if it was non-0:
select typeof(ceil(cast(1 as decimal(38, 1))));
result: DECIMAL(38,0)

select typeof(ceil(cast(1 as decimal(38, 37))));
result: DECIMAL(2,0)

Hive works the same way as Impala.

Generally ceil/floor/round is NOOP for integer types (and decimals with scale 0)

Note that I don't know how other databases handle this, e.g. https://docs.microsoft.com/en-us/sql/t-sql/functions/round-transact-sql?view=sql-server-ver15 says
Expression result Return type
decimal and numeric category (p, s) decimal(p, s)

which looks very different than the way we work.