[jira] [Created] (FLINK-31729) Unexpected UPDATE_BEFORE output record in LEFT OUTER JOIN

["Alexander Smirnov (Jira)" <ji...@apache.org>]

Alexander Smirnov created FLINK-31729:
-----------------------------------------

             Summary: Unexpected UPDATE_BEFORE output record in LEFT OUTER JOIN
                 Key: FLINK-31729
                 URL: https://issues.apache.org/jira/browse/FLINK-31729
             Project: Flink
          Issue Type: Bug
          Components: Table SQL / Runtime
    Affects Versions: 1.17.0
            Reporter: Alexander Smirnov
             Fix For: 1.18.0
         Attachments: image-2023-04-05-00-08-32-984.png

Currently, in streaming LEFT/RIGHT/FULL OUTER JOIN Flink SQL doesn't emit UPDATE_BEFORE/UPDATE_AFTER records, but instead explicitly change RowKind of output records to INSERT/DELETE for simplicity. However, it doesn't work as expected, because sometimes UPDATE_BEFORE rows can be emitted. What is more confusing - after UPDATE_BEFORE record there will be INSERT record (not UPDATE_AFTER), which can cause bugs in case when downstream operators process UPDATE records in a different way than INSERT/DELETE (for example, it can assume, that after UPDATE_BEFORE there should be UPDATE_AFTER record at some point of time).

How to reproduce:

Suppose we have tables "source1" and "source2":
CREATE TABLE source1(
  id int PRIMARY KEY,
  c3 bigint
) WITH (
  'connector' = 'kafka',
   ...
  'format' = 'debezium-json'
);

 

CREATE TABLE source2(
  id int PRIMARY KEY,
  c3 bigint
) WITH (
  'connector' = 'kafka',
   ...
  'format' = 'debezium-json'
);

And we execute the following query:
"select  t1.id, t1.c3,t2.id, t2.c3 from source1 t1 left join source2 t2 on t1.id = t2.id"

Then we insert records one by one:
source1: \{"before":null,"after":{"id":2,"c3":7121},"op":"c"}
source2: \{"before":null,"after":{"id":2,"c3":364},"op":"c"}
source1: \{"before":{"id":2,"c3":7121},"after":\{"id":2,"c3":7222},"op":"u"}
source2: \{"before":{"id":2,"c3":364},"after":\{"id":2,"c3":564},"op":"u"}

The result will be as in the following screenshot:

!image-2023-04-05-00-08-32-984.png!


Note, that after implementing ticket https://issues.apache.org/jira/browse/FLINK-17337 (support emitting UPDATE_BEFORE/UPDATE_AFTER records not only in inner join) the described error won't be relevant anymore.



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