Support better updates by using MERGE with PostgreSQL

[thadguidry]

https://www.postgresql.org/docs/current/sql-merge.html

I want to use a where condition to update, insert, or delete the candidate rows on a schema-qualified target table, for instance, WHEN NOT MATCHED BY TARGET, could be implemented with support syntax such as merge=matched to merge when candidate rows from the data_source match the target table. Or merge=out=table2 ?

This needs more thought on syntax for ease of use, but at least documents the use case of simplifying modifying rows in a target table based on joining it with a data source and evaluating matching rows between them (candidate rows) and then choosing a merge action such as update, insert, delete.