Unity catalog exporter: Exported tables should retain original table field documentation

[talSofer]

databricks users can add comments to tables in Unity Catalog and to their columns for documentation purposes. Table-level comments can be added after table creation, but column-level comments can be added on table creation.

Currently, table and column comments don't survive the export process to Unity Catalog.

Requirements

• Retain Delta Lake tables comments on their export to Unity
• Retain Delta Lake columns comments on their export to Unity

[itaiad200]

Why is this a bug for exported tables only? AFAICT @kesarwam opened the issue before we exported the tables

[talSofer]

@itaiad200 this is not a bug, this is an enhancement request. The way I see this, we should not support this for Unity delta sharing solution (against which #6322 was opened) but include it in our recommended delta + unity solution which is the exporter. Makes sense?

[Jonathan-Rosenberg]

Column comments are already supported:

[Jonathan-Rosenberg]

So currently Delta table comments (both on table and column) are exported. When running:

1. DESCRIBE DETAIL <catalog>.<schema>.<table>; you'll get the table comment (although you can't see it in the Unity GUI).
2. DESCRIBE TABLE <catalog>.<schema>.<table>; you'll get the column comments (you can also see it in the Unity GUI).

LMK if you wish me to keep working on that @talSofer @ozkatz

[talSofer]

Great news @Jonathan-Rosenberg! Do you know what effort does it take to make table documentation appear in the Unity catalog UI?

[Jonathan-Rosenberg]

not much... Just wanted to know that it's indeed necessary