[jira] [Resolved] (IMPALA-13262) Predicate pushdown causes incorrect results in join condition

["Fang-Yu Rao (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-13262?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Fang-Yu Rao resolved IMPALA-13262.
----------------------------------
    Resolution: Fixed

The fix has been merged to master.

> Predicate pushdown causes incorrect results in join condition
> -------------------------------------------------------------
>
>                 Key: IMPALA-13262
>                 URL: https://issues.apache.org/jira/browse/IMPALA-13262
>             Project: IMPALA
>          Issue Type: Bug
>            Reporter: Fang-Yu Rao
>            Assignee: Fang-Yu Rao
>            Priority: Major
>              Labels: correctness
>             Fix For: Impala 4.5.0
>
>
> We found that in some scenario Apache Impala ([https://github.com/apache/impala/commit/c539874]) could incorrectly push predicates to scan nodes, which in turn produces the wrong result. The following is a concrete example to reproduce the issue.
> {code:sql}
> create database impala_13262;
> use impala_13262;
> create table department ( dept_no integer, dept_rank integer, start_date timestamp,end_date timestamp);
> insert into department values(1,1,'2024-01-01','2024-01-02');
> insert into department values(1,2,'2024-01-02','2024-01-03');
> insert into department values(1,3,'2024-01-03','2024-01-03');
> create table employee (employee_no integer, depart_no integer);
> insert into employee values (1,1);
> // The following query should return 0 row. However Apache Impala produces one row.
> select * from employee t1
> inner join (
> select * from
> (
> select dept_no,dept_rank,start_date,end_date
> ,row_number() over(partition by dept_no order by dept_rank) rn
> from department
> ) t2
> where rn=1
> ) t2
> on t1.depart_no=t2.dept_no
> where t2.start_date=t2.end_date;
> set explain_level=2;
> // In the output of the EXPLAIN statement, we found that the predicate "start_data = end_date" was pushed
> // down to the scan node, which is wrong.
> | 01:SCAN HDFS [impala_13262.department, RANDOM]                                                        |
> |    HDFS partitions=1/1 files=3 size=132B                                                              |
> |    predicates: start_date = end_date                                                                  |
> |    stored statistics:                                                                                 |
> |      table: rows=unavailable size=unavailable                                                         |
> |      columns: unavailable                                                                             |
> |    extrapolated-rows=disabled max-scan-range-rows=unavailable                                         |
> |    mem-estimate=32.00MB mem-reservation=8.00KB thread-reservation=1                                   |
> |    tuple-ids=1 row-size=40B cardinality=1                                                             |
> |    in pipelines: 01(GETNEXT)                                                                          |
> +-------------------------------------------------------------------------------------------------------+
> {code}
>  
> +*Edit:*+
> The following is a smaller case to reproduce the issue. The correct result should be 0 row but Impala returns 1 row as above.
> {code:java}
> select * from
> (
> select dept_no,dept_rank,start_date,end_date
> ,row_number() over(partition by dept_no order by dept_rank) rn
> from department
> ) t2
> where rn=1 and t2.start_date=t2.end_date;
> {code}
>  
> Recall the contents of the inline view '{*}t2{*}' above is as follows.
> {code:java}
> +---------+-----------+---------------------+---------------------+----+
> | dept_no | dept_rank | start_date          | end_date            | rn |
> +---------+-----------+---------------------+---------------------+----+
> | 1       | 1         | 2024-01-01 00:00:00 | 2024-01-02 00:00:00 | 1  |
> | 1       | 2         | 2024-01-02 00:00:00 | 2024-01-03 00:00:00 | 2  |
> | 1       | 3         | 2024-01-03 00:00:00 | 2024-01-03 00:00:00 | 3  |
> +---------+-----------+---------------------+---------------------+----+
> {code}
>  
> On the other hand, the following query without the conjunct '{*}rn=1{*}' returns the correct result, which is the row with '{*}rn{*}' equal to *3* above. It almost looks like adding this '{*}rn=1{*}' predicate triggers the incorrect pushdown of '{*}t2.start_date=t2.end_date{*}' to the scan node of the table '{*}department{*}'.
> {code:java}
> select * from
> (
> select dept_no,dept_rank,start_date,end_date
> ,row_number() over(partition by dept_no order by dept_rank) rn
> from department
> ) t2
> where t2.start_date=t2.end_date;
> {code}



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