Unless the client uses the SKIP_METADATA flag,
Scylla attaches some metadata to query results returned to the CQL
client.
In particular, it attaches the spec (keyspace name, table
name, name, type) of the returned columns.
By default, the keyspace name and table name is present in each column
spec. However, since they are almost always the same for every column
(I can't think of any case when they aren't the same;
it would make sense if Cassandra supported joins, but it doesn't)
that's a waste.
So, as an optimization, the CQL protocol has the GLOBAL_TABLES_SPEC flag.
The flag can be set if all columns belong to the same table,
and if is set, then the keyspace and table name are only written
in the first column spec, and skipped in other column specs.
Scylla sets this flag, if appropriate, in responses to a PREPARE requests.
But it never sets the flag in responses to queries.
But it could. And this patch causes it to do that.
Fixes#17788Closesscylladb/scylladb#25205
6d27065f99