Alter table supports rename columns

[killme2008]

What problem does the new feature solve?

GreptimeDB already supports altering table schema by adding, removing columns or renaming the table name. But we don't support renaming columns.

For example:

ALTER TABLE table_name
RENAME COLUMN old_name TO new_name;

What does the feature do?

Rename a column name by alter statement.

Implementation challenges

Do we allow renaming a time index column? If so, there are some tricky problems that have to be processed：

• The old data before renaming can be read.
• Flushing and compaction work properly in this case.

[killme2008]

It's not done.

[NiwakaDev]

Does greptimedb have plans to support modify or already have something similar? I'd like to use not only this but also modify:

alter table test_table modify column_name double not null;

I'd like to change null constraint for columns.

[MichaelScofield]

I'm afraid column alternation is not an easy task. @evenyag can you confirm that?

[evenyag]

Does greptimedb have plans to support modify or already have something similar? I'd like to use not only this but also modify:

alter table test_table modify column_name double not null;

I'd like to change null constraint for columns.

It is hard to modify a column from nullable to not nullable since existing data may contain null. Changing a not null column to nullable is easier.

[KKould]

I think this is very relevant to https://github.com/GreptimeTeam/greptimedb/issues/3517

[killme2008]

I think this is very relevant to #3517

Yes, relevant to column metadata changing.