Prefer oldest version in ReplacingMergeTree - clickhouse

Question

I have a maybe slightly weird use case. I have to perform expansive counts on data and build snapshots from them (something like "number of users who can access this entity"). Now I store these numbers per entity with a timestamp (so basically "at this point in time, x users could access this entity").
Now it might be, that the number doesn't change between snapshots, because no access lists have been changed and/or no users have been added. This might actually even be the default case. So of course I would like to avoid having tens of thousands of identical lines ("5 users at 10pm", "5 users at 11pm", "5 users at 12pm" and so on). Therefore a ReplacingMergeTree comes to mind. The order by would be entity, count.
There is a problem though. If I understand the documentation correctly, the ReplacingMergeTree would now keep always the latest row. So the timestamp would change. While I would like to keep the oldest timestamp, so I know the first time this count has been calculated. This in turn I can use to fill the gaps (if the count is 3h old and there is no newer count in between, obviously the same count can be assumed true for 2h ago and 1h ago).
Is there any way to achieve this?
The only thing that might come to mind might be using a uint as version and starting with MaxUint and then decrementing. But this feels slightly weird.

Answer 1

best way I found until now is add a version column: UInt32 DEFAULT 4294967295 - toUnixTimestamp(create_time)
CREATE TABLE test
(
`id` UInt8,
`value` UInt8,
`version` UInt32 DEFAULT 4294967295 - toUnixTimestamp(create_time),
`create_time` DateTime DEFAULT now()
)
ENGINE = ReplacingMergeTree(version)
ORDER BY id;
INSERT INTO test (id, value) VALUES (1,1);
INSERT INTO test (id, value) VALUES (1,2);
SELECT * FROM test;
┌─id─┬─value─┬────version─┬─────────create_time─┐
│ 1 │ 1 │ 2670403264 │ 2021-06-25 03:47:11 │
└────┴───────┴────────────┴─────────────────────┘
┌─id─┬─value─┬────version─┬─────────create_time─┐
│ 1 │ 2 │ 2670403251 │ 2021-06-25 03:47:24 │
└────┴───────┴────────────┴─────────────────────┘
SELECT * FROM test FINAL;
┌─id─┬─value─┬────version─┬─────────create_time─┐
│ 1 │ 1 │ 2670403264 │ 2021-06-25 03:47:11 │
└────┴───────┴────────────┴─────────────────────┘