Paul Rogers created IMPALA-7964:
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Summary: Inconsistent typing of pure-constant expressions
Key: IMPALA-7964
URL: https://issues.apache.org/jira/browse/IMPALA-7964
Project: IMPALA
Issue Type: Bug
Components: Frontend
Affects Versions: Impala 3.1.0
Reporter: Paul Rogers
Assignee: Paul Rogers
Impala implements a very subtle rule for computing the type of constant
expressions. See IMPALA-4213. The desired rules when performing constant
folding are:
* Pure-literal numeric expressions take the natural (smallest) type of the
result.
* All other expressions preserve the type of the expression.
Examples:
{noformat}
-- simple literal
100 -> 100:TINYINT
-- explicit cast
CAST(100 AS SMALLINT) --> 100:SMALLINT
-- pure literal expression
2 + 3 --> 5:TINYINT
-- addition is done at next wider type up from that of tinyint_col
tinyint_col + 3 --> SMALLINT
-- explicit type given, math done with that type, mimics above
CAST(2 AS TINYINT) + 3 --> 5:SMALLINT
-- Impala uses C++ semantics, with overflow
CAST(257 AS TINYINT) --> 2:TINYINT
{noformat}
At present, some parts of the code follow these rules, but the constant folding
rule does not. As a result, {{PlannerTest}} fails for subtle changes in
unrelated areas. Some {{PlannerTest}} results, such as the Kudu test mentioned
in IMPALA-4213 do observe the rules. But, some constant folding test *do not*
observe the rules.
Expected that the rules would be followed on all code paths to ensure
consistent results.
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