[Bug] fall-back branch does not work

[JackeyLee007]

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• I searched in the issues and found nothing similar.

Paimon version

1.0-SNAPSHOT

Compute Engine

flink 1.18.1

Minimal reproduce step

Just as the steps described in doc

CREATE TABLE T (
    dt STRING NOT NULL,
    name STRING NOT NULL,
    amount BIGINT
) PARTITIONED BY (dt);

-- create a branch for streaming job
CALL sys.create_branch('default.T', 'test');

-- set primary key and bucket number for the branch
ALTER TABLE `T$branch_test` SET (
    'primary-key' = 'dt,name',
    'bucket' = '2',
    'changelog-producer' = 'lookup'
);

-- set fallback branch
ALTER TABLE T SET (
    'scan.fallback-branch' = 'test'
);

-- write records into the streaming branch
INSERT INTO `T$branch_test` VALUES ('20240725', 'apple', 4), ('20240725', 'peach', 10), ('20240726', 'cherry', 3), ('20240726', 'pear', 6);

-- write records into the default branch
INSERT INTO T VALUES ('20240725', 'apple', 5), ('20240725', 'banana', 7);

SELECT * FROM T;



### What doesn't meet your expectations?

Expect union result from both T and T$branch_test, like the following:
/*
+------------------+------------------+--------+
|               dt |             name | amount |
+------------------+------------------+--------+
|         20240725 |            apple |      5 |
|         20240725 |            peach|     10|
|         20240725 |           banana |      7 |
|         20240726 |           cherry |      3 |
|         20240726 |             pear |      6 |
+------------------+------------------+--------+
*/

But only got data from T,

/*
+------------------+------------------+--------+
|               dt |             name | amount |
+------------------+------------------+--------+
|         20240725 |            apple |      5 |
|         20240725 |           banana |      7 |
+------------------+------------------+--------+
*/

### Anything else?

Only got union result after fast-forward:
CALL sys.fast_forward('default.T', 'test');

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

[gmdfalk]

isn't that expected behaviour?
until you do a fast_forward the main branch T will be completely separate from T$branch_test and thus selecting from it will not show any union of the 2 separate branches.

[JackeyLee007]

It's Not Expected according to the document.
It should union the found partition with the fallback branch, that's the reason why invent fallback branch.

[JackeyLee007]

Sorry for the missleading. It's my fault.
The fallback query should be executed in batch mode, not streaming mode.