Joe McDonnell created IMPALA-11323:
--------------------------------------
Summary: Invalid inferred predicates based on null values being
equivalent
Key: IMPALA-11323
URL: https://issues.apache.org/jira/browse/IMPALA-11323
Project: IMPALA
Issue Type: Bug
Components: Frontend
Affects Versions: Impala 4.2.0
Reporter: Joe McDonnell
This query should return two rows, but instead it returns nothing:
{noformat}
[localhost:21050] default> with t as (select 1 a), v as (select distinct a,
cast(null as smallint)b, cast(null as smallint)c from t) select distinct a,b,c
from v union all select distinct a,b,c from v;
Fetched 0 row(s) in 0.14s{noformat}
Without the union all, each side is producing a single row, so it stands to
reason that the union all would produce two rows:
{noformat}
[localhost:21050] default> with t as (select 1 a), v as (select distinct a,
cast(null as smallint)b, cast(null as smallint)c from t) select distinct a,b,c
from v;
+---+------+------+
| a | b | c |
+---+------+------+
| 1 | NULL | NULL |
+---+------+------+
Fetched 1 row(s) in 0.14s
{noformat}
Both b and c are hard coded to null in the definition of v. The plan shows that
it is producing a b = c predicate:
{noformat}
+-------------------------------------------------------------------+
| Explain String |
+-------------------------------------------------------------------+
| Max Per-Host Resource Reservation: Memory=7.88MB Threads=1 |
| Per-Host Resource Estimates: Memory=24MB |
| Codegen disabled by planner |
| |
| PLAN-ROOT SINK |
| | |
| 00:UNION |
| | pass-through-operands: all |
| | row-size=5B cardinality=2 |
| | |
| |--08:SELECT |
| | | predicates: b = c |
| | | row-size=5B cardinality=1 |
| | | |
| | 07:AGGREGATE [FINALIZE] |
| | | group by: a, CAST(NULL AS SMALLINT), CAST(NULL AS SMALLINT) |
| | | row-size=5B cardinality=1 |
| | | |
| | 06:AGGREGATE [FINALIZE] |
| | | group by: a, CAST(NULL AS SMALLINT) |
| | | row-size=3B cardinality=1 |
| | | |
| | 05:UNION |
| | constant-operands=1 |
| | row-size=1B cardinality=1 |
| | |
| 04:SELECT |
| | predicates: b = c |
| | row-size=5B cardinality=1 |
| | |
| 03:AGGREGATE [FINALIZE] |
| | group by: a, CAST(NULL AS SMALLINT), CAST(NULL AS SMALLINT) |
| | row-size=5B cardinality=1 |
| | |
| 02:AGGREGATE [FINALIZE] |
| | group by: a, CAST(NULL AS SMALLINT) |
| | row-size=3B cardinality=1 |
| | |
| 01:UNION |
| constant-operands=1 |
| row-size=1B cardinality=1 |
+-------------------------------------------------------------------+
{noformat}
I added tracing to PlanNode's addConjunctsToNode() and the b=c conjunct is
generated by Analyzer::createEquivConjuncts(). It survives the inferred
identity predicate checks, because it is referring to two different slots.
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