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https://issues.apache.org/jira/browse/IMPALA-13262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17875012#comment-17875012
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Fang-Yu Rao edited comment on IMPALA-13262 at 8/19/24 11:01 PM:
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Thanks [~MikaelSmith]!
{quote}Wouldn't that limit the ScanNode to return only the 3rd row?
{quote}
This is correct. If we push the predicate '{*}start_date = end_date{*}' to the
scan node of the table '{*}department{*}' we will get the 3rd row as shown
below.
{code:java}
+---------+-----------+---------------------+---------------------+
| dept_no | dept_rank | start_date | end_date |
+---------+-----------+---------------------+---------------------+
| 1 | 3 | 2024-01-03 00:00:00 | 2024-01-03 00:00:00 |
+---------+-----------+---------------------+---------------------+
{code}
Later on when we apply the analytic function '{*}row_number(){*}' to this
returned row, this row above would be associated with the row number of 1, thus
satisfying the (analytic) conjunct of '{*}rn = 1{*}' and we would get this row
as a result.
However, if we do not push the predicate '{*}start_date = end_date{*}' to the
scan node of the table '{*}department{*}', we will get all 3 rows, on which we
will apply the analytic function '{*}row_number(){*}'. This time the row that
is associated with the row number of 1 is different. And this row of row number
1 does not satisfy '{*}start_date = end_date{*}' so no row would be returned.
{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}
was (Author: fangyurao):
Thanks [~MikaelSmith]!
{quote}Wouldn't that limit the ScanNode to return only the 3rd row?
{quote}
This is correct. If we push the predicate '{*}start_date = end_date{*}' to the
scan node of the table '{*}department{*}' we will get the 3rd row as shown
below.
{code:java}
+---------+-----------+---------------------+---------------------+
| dept_no | dept_rank | start_date | end_date |
+---------+-----------+---------------------+---------------------+
| 1 | 3 | 2024-01-03 00:00:00 | 2024-01-03 00:00:00 |
+---------+-----------+---------------------+---------------------+
{code}
Later on when we apply the analytic function '{*}row_number(){*}' to this
returned row, this row above would be associated with the row number of 1, thus
satisfying the (analytic) conjunct of '{*}rn = 1{*}' and we would get this row
as a result.
However, if we do not push the predicate '{*}start_date = end_date{*}' to the
scan node of the table '{*}department{*}', we will get all 3 rows, on which we
will apply the analytic function '{*}row_number(){*}'. This time the row that
is associated with the row number of 1 is different. And this row of row number
1 does not satisfy '{*}start_date = end_date{*}'.
{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}
> 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
>
> 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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