Paul Rogers created IMPALA-7793:
-----------------------------------
Summary: CASE statement does not handle NULL from UDF overflow
Key: IMPALA-7793
URL: https://issues.apache.org/jira/browse/IMPALA-7793
Project: IMPALA
Issue Type: Bug
Components: Backend
Affects Versions: Impala 3.0
Reporter: Paul Rogers
The test suite {{QueryTest/decimal-exprs}} contains the following test:
{code:sql}
set decimal_v2=false;
set ENABLE_EXPR_REWRITES=false;
select coalesce(1.8, cast(0 as decimal(38,38)))
{code}
Which produces this result:
{noformat}
+------------------------------------------+
| coalesce(1.8, cast(0 as decimal(38,38))) |
+------------------------------------------+
| 0.00000000000000000000000000000000000000 |
+------------------------------------------+
WARNINGS: UDF WARNING: Decimal expression overflowed, returning NULL
{noformat}
Notice that the "1.8" overflowed when being put into a {{DECIMAL(38,38)}} type.
(The precision and range are both 38, meaning all digits are after the decimal
point.)
The {{coalesce()}} function caught the overflow, treated it as a {{NULL}}, and
selected the second value from the list, which is 0.
Very good. Now, try the equivalent CASE form (from MPALA-7655):
{noformat}
select CASE WHEN 1.8 IS NOT NULL THEN 1.8 ELSE cast(0 as decimal(38,38)) END;
+-----------------------------------------------------------------------+
| case when 1.8 is not null then 1.8 else cast(0 as decimal(38,38)) end |
+-----------------------------------------------------------------------+
| NULL |
+-----------------------------------------------------------------------+
WARNINGS: UDF WARNING: Decimal expression overflowed, returning NULL
{noformat}
Apparently, the overflow somehow caused the {{ELSE}} clause to not fire.
This one is likely a bug in the BE code generation. Though, tried the {{CASE}}
query with a variety of options:
{noformat}
set disable_codegen=true;
and
set disable_codegen=false;
set disable_codegen_rows_threshold=0;
and
set disable_codegen_rows_threshold=10;
{noformat}
In all cases, the {{CASE}} produced the wrong result. Also tried wrapping the
expression {{1.8 IS NOT NULL}} in a variety of forms: {{IS TRUE}}, {{IS NOT
FALSE}}. None of this worked correctly.
The result of this bug is the the above-mentioned test case fails in a build
that contains MPALA-7655.
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