Deprecate the implementation of deduplicate that uses a natural join

[dbeatty10]

Describe the bug

The current default implementation of deduplicate uses a natural join that is not null safe.

After the next release, this issue won't affect bigquery, databricks, postgres, redshift, or snowflake, because they will each have their own null safe implementation that will override the default.

#815 contains alternative approaches that will allow the user to choose a null safe option that is most appropriate for them. In addition to that, we want to get the not safe implementation on a deprecation path.

Then in a future version, we should raise an error to replace the deprecation warning.

System information

The contents of your packages.yml file:

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: only affects adapters other than the above)

Are you interested in contributing the fix?

Yep 👍

[github-actions]

This issue has been marked as Stale because it has been open for 180 days with no activity. If you would like the issue to remain open, please comment on the issue or else it will be closed in 7 days.

[github-actions]

This issue has been marked as Stale because it has been open for 180 days with no activity. If you would like the issue to remain open, please comment on the issue or else it will be closed in 7 days.

[github-actions]

Although we are closing this issue as stale, it's not gone forever. Issues can be reopened if there is renewed community interest. Just add a comment to notify the maintainers.