This looks it takes an entire column and upserts all of its rows into another column, on the same or another table.
Is that correct? Is this part of the SQL standard? Is this the same as MERGE in SQL Server and Oracle (which has no counterpart in MySQL)?
IIRC upsert in PG is different than in Mysql, MS or Oracle; is that the same here?
Are there any good resources for this?
(Microsoft seems to have added a BY TARGET/BY SOURCE specification to the WHEN NOT MATCHED clause, which is not in the standard. Oracle seems to do DELETE in a different, nonstandard way.)
"Upsert" (which is called INSERT ON CONFLICT UPDATE in Postgres) is a different animal. It is not part of the SQL standard, which is why every database system does its own stuff.
Merge acts on multiple rows and columns at the same time.