[FLINK-19649][sql-parser] Fix unparse method of sql create table. Keep syntax the same for tables without columns

[gsralex]

What is the purpose of the change

In Flink's module flink-sql-parser, the sqlCreateTable.class unparse method the create table statement does not match the new rules of the print connector.

The print connector supports this:

CREATE TABLE table_print WITH ('connector' = 'print') LIKE table (EXCLUDING ALL)

When a print table is created without any columns, the parentheses must be omitted.

However, the unparse generated statements in SqlCreateTable contain parentheses. This will affect the SqlCreateTable.toString() ,SqlCreateTable.toSqlString() methods.

CREATE TABLE table_print() WITH ('connector' = 'print') LIKE table (EXCLUDING ALL)  

Might need to add the following to the unparse method for columnList.size > 0.

Brief change log

• Add the following to the unparse method for columnList.size > 0.
• Add unit tests to unparse methods to create tables without columns.

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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• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, 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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Last check on commit 049be6b (Fri Oct 16 10:57:23 UTC 2020)

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[KurtYoung]

Please add some unit tests.

[gsralex]

Please add some unit tests.

Okay, I'll add some unit tests.

[gsralex]

Please add some unit tests.

Okay, I'll add some unit tests.

Hi, Kurt. I've added some unit tests.

[KurtYoung]

Thanks for the fix, LGTM