[FLINK-19883][table] Support 'IF EXISTS' in DDL for ALTER TABLE

[SteNicholas]

What is the purpose of the change

ALTER TABLE does not seem to support the IF EXISTS part in the DDL, but the corresponding methods Catalog#renameTable and Catalog#alterTable do support it. Flink DDL should support IF EXISTS in DDL for ALTER TABLE.

Brief change log

• Add the IF EXISTS syntax support for the ALTER TABLE DDL.

Verifying this change

• SqlToOperationConverterTest, CatalogTableITCase and table.q add the tests for ALTER TABLE IF EXISTS syntax.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
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• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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[Airblader]

Thanks for picking this up. I gave this a first round of review! :-)

[SteNicholas]

@wuchong @Airblader , I have addressed the comments mentioned above. Please help to review again.

[Airblader]

I'm still not really happy with this; now we added redundant information for the sake of the summary string, but this information isn't actually used by CatalogManager to alter the table.

In principle I think this class shouldn't hold a CatalogTable at all, but rather only an identifier (which it already does from its superclass) and the new options to be added. TableEnvironmentImpl#executeInternal then just looks up the table when needed (as it already does for some other operations).

Happy to hear someone else's thoughts on this as well.

[SteNicholas]

@Airblader , the CatalogTable isn't hold only by AlterTableOptionsOperation. Other operations like AlterTableSchemaOperation also hold the CatalogTable.
IMO, the converter between the SQL and operation should not pass the CatalogTable. The CatalogTable is looked up when calling TableEnvironmentImpl#executeInternal. But the changes could be pushed another PR to unify for updating.
cc @wuchong

[Airblader]

Yes, other operations do that, too, and probably shouldn't do it either. The design of operations needs to be improved overall, because both the operations and the converter contain way too much logic. I think it would be good to improve this for this operation with this PR, because we kind of need it. Otherwise we'd have either incorrectness or redundancy, and both would be a worse situation than before.

I don't think it's a big change to fix this here. It's a pretty small change to just look up the table in TableEnvironmentImpl instead of passing it to the operation during the conversion.

[SteNicholas]

@Airblader , OK, I would like to change for this.

[lsyldliu]

Thanks for your contribution @SteNicholas, Can you continue to finish this work?

[SteNicholas]

Thanks for your contribution @SteNicholas, Can you continue to finish this work?

@lsyldliu, thanks for the reminder. I will update this pull request this week. Sorry for the delay to update.

[LadyForest]

Thanks for your contribution @SteNicholas, Can you continue to finish this work?

@lsyldliu, thanks for the reminder. I will update this pull request this week. Sorry for the delay to update.

Hi @SteNicholas, would you like to continue this task?