An example in the materialized view documentation [1] includes an ORDER BY clause without a clear reason. Does it help build the index more efficiently? I suppose it's also sort of like a CLUSTER?
But it seems like the ORDER BY should either be explained or dropped: as is, this gives the impression that the ORDER BY can be "embedded" into the resulting relation and persist to other queries that do not include an explicit ORDER BY. (I recently ran across this belief, though not sure if this was due to this example.)