Eng 6396 upsert ad hoc

Another good test here would be to use `UPSERT INTO ... SELECT` where some of the rows produced by the select will require updates, and some will require inserts, as in:

```SQL
INSERT INTO t1 SELECT <rows 1 - 10 from some other table>;
UPSERT INTO t1 SELECT <rows 5 - 15 from some other table>;
```