Set the table comment when creating the table

[Fokko]

This avoids a schema change in Iceberg when dbt does an:

comment on table sandbox.dbt_trino.rides is 'Combined table of NYC Taxi rides with the locations'

Because the comment is already there.

Overview

Checklist

• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• README.md updated and added information about my change
• I have run changie new to create a changelog entry

[hovaesco]

Can you add a test or modifying existing one for that ?

[Fokko]

@hovaesco This is already tested by TestPersistDocsTable

[hovaesco]

@Fokko please squash the commits

[damian3031]

@Fokko could you explain a little bit more why this change is needed? What is wrong with current behaviour?

[Fokko]

@damian3031 Certainly. In Iceberg we keep track of the changes to a schema. If you set the table comment:

{{ config(
  persist_docs={"relation": true},
  file_format="iceberg"
) }}

This will first create the table:

create table sandbox.dbt_trino.rides__dbt_tmp
      comment 'Combined table of NYC Taxi rides with the locations'

And then later it will do an:

comment on table sandbox.dbt_trino.rides is 'Combined table of NYC Taxi rides with the locations'

With this change, the comment will be set on table creation. When the COMMENT ON is being executed, it is actually a no-op for Iceberg, because nothing changes since the comment is already there. This avoids updating the schema on the Iceberg side (and also increases performance, because it doesn't have to write the updated metadata json).

I'm hesitant to remove the comment on because if you change the comment, and you use an incremental strategy, it would need to detect that the comment has changed. Unfortunately, the comment is not part of the dbt relation object, so I think it is best to keep the redundant COMMENT ON in there for now.