Add change to VARCHAR in the upgrade guide

[alamb]

Which issue does this PR close?

• Related to Change mapping of SQL VARCHAR from Utf8 to Utf8View #15096
• Follow on to Change default SQL mapping for VARCAHR from Utf8 to Utf8View #16142

Rationale for this change

Let's add some documentation to the upgrade guide about the change in #16142

What changes are included in this PR?

Upgrade guide updates

Are these changes tested?

Are there any user-facing changes?

[zhuqi-lucas]

Thank you @alamb , i think we also need to add note:

If customers use avro format, for datafusion 48.0, we need to set datafusion.sql_parser.map_varchar_to_utf8view = false;

Because the support for utf8view for avro are not releasing currently.

apache/arrow-rs#7262

[alamb]

Than you @zhuqi-lucas -- good call. Hopefully by the time we release Datafusion 48 the upstream supprt for avro will be released too.

[comphead]

lgtm thanks @alamb

I remember back then in Oracle days, there was VARCHAR and VARCHAR2 data types, just thinking aloud if it can be reused like VARCHAR is UTF8 ArrowType, VARCHAR2 is UTF8View

[zhuqi-lucas]

lgtm thanks @alamb

I remember back then in Oracle days, there was VARCHAR and VARCHAR2 data types, just thinking aloud if it can be reused like VARCHAR is UTF8 ArrowType, VARCHAR2 is UTF8View

Interesting @comphead , we are currently have the option to disable it and fall back to UTF8:
set datafusion.sql_parser.map_varchar_to_utf8view = false;

But it seems if we also have the VARCHAR/VARCHAR2 , it's also a improvement from customer side. Thanks!

[alamb]

I remember back then in Oracle days, there was VARCHAR and VARCHAR2 data types, just thinking aloud if it can be reused like VARCHAR is UTF8 ArrowType, VARCHAR2 is UTF8View

Thanks @comphead -- this is an interesting idea. I think if there is strong demand to make it easier to distinguish between Utf8 and Utf8View it is worth pursuing that.

[alamb]

Had to merge this so we had at least one commit today 😅

[alamb]

Thanks @comphead and @zhuqi-lucas