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c72058199f
This patch fixes #12475, where an aggregation (e.g., COUNT(*), MIN(v))
of absolutely no partitions (e.g., "WHERE p = null" or "WHERE p in ()")
resulted in an internal error instead of the "zero" result that each
aggregator expects (e.g., 0 for COUNT, null for MIN).
The problem is that normally our aggregator forwarder picks the nodes
which hold the relevant partition(s), forwards the request to each of
them, and then combines these results. When there are no partitions,
the query is sent to no node, and we end up with an empty result set
instead of the "zero" results. So in this patch we recognize this
case and build those "zero" results (as mentioned above, these aren't
always 0 and depend on the aggregation function!).
The patch also adds two tests reproducing this issue in a fairly general
way (e.g., several aggregators, different aggregation functions) and
confirming the patch fixes the bug.
The test also includes two additional tests for COUNT aggregation, which
uncovered an incompatibility with Cassandra which is still not fixed -
so these tests are marked "xfail":
Refs #12477: Combining COUNT with GROUP by results with empty results
in Cassandra, and one result with empty count in Scylla.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes #12715
(cherry picked from commit 3ba011c2be)