The `select` part operates not over a single record, but over each group
(i.e., the set of records sharing the same group key). The `select`
clause's environment is generally:
* `name` (the group key)
* `group` (the table of records in the group)
Note: no `p` is bound (`p` is not set; it was the row variable during scan, but we are now at the group level).
In the `select { name = name }` the name refers to the group key (what
we `group by`-ed).
We typically use:
* `name = name` (group key, as in the query), or
* if we want data from the first record (say all grouped `p.name` are
the same and non-`nil`) then `name = group[1].name`.
Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>
Matouš Jan Fialka
b6d4f71aca