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In issue #10767, concerned were raised that the CLUSTERING ORDER BY clause is handled incorrectly in a CREATE MATERIALIZED VIEW definition. The tests in this patch try to explore the different ways in which CLUSTERING ORDER BY can be used in CREATE MATERIALIZED VIEW and allows us to compare Scylla's behaivor to Cassandra, and to common sense. The tests discover that the CLUSTERING ORDER BY feature in materialized views generally works as expected, but there are *three* differences between Scylla and Cassandra in this feature. We consider two differences to be bugs (and hence the test is marked xfail) and one a Scylla extension: 1. When a base table has a reverse-order clustering column and this clustering column is used in the materialized view, in Cassandra the view's clustering order inherits the reversed order. In Scylla, the view's clustering order reverts to the default order. Arguably, both behaviors can be justified, but usually when in doubt we should implement Cassandra's behavior - not pick a different behavior, even if the different behavior is also reasonable. So this test (test_mv_inherit_clustering_order()) is marked "xfail", and a new issue was created about this difference: #12308. If we want to fix this behavior to match Cassandra's we should also consider backward compatibility - what happens if we change this behavior in Scylla now, after we had the opposite behavior in previous releases? We may choose to enshrine Scylla's Cassandra- incompatible behavior here - and document this difference. 2. The CLUSTERING ORDER BY should, as its name suggests, only list clustering columns. In Scylla, specifying other things, like regular columns, partition-key columns, or non-existent columns, is silently ignored, whereas it should result in an Invalid Request error (as it does in Cassandra). So test_mv_override_clustering_order_error() is marked "xfail". This is the difference already discovered in #10767. 3. When a materialized view has several clustering columns, Cassandra requires that a CLUSTERING ORDER BY clause, if present, must specify the order of all of *all* clustering columns. Scylla, in contrast, allows the user to override the order of only *some* of these columns - and the rest get the default order. I consider this to be a legitimate Scylla extension, and not a compatibility bug, so marked the test with "scylla_only", and no issue was opened about it. Refs #10767 Refs #12308 Signed-off-by: Nadav Har'El <nyh@scylladb.com> Closes #12307