See #17293 (comment)

> FWIW I mildly prefer the styling `? < a AND a <= ?` as then my brain can more easily convert that to `a in (?...?]`

…the last event

Previously, it would use the event with the lowest `stream_ordering` that was
fetched (we want the highest `stream_ordering. `union` does not work how you
might think at first and does not preserve the ordering of the operand queries.

`union all` also doesn't necessarily have that gurantee but it does behave
that way. See https://dba.stackexchange.com/questions/316818/are-results-from-union-all-clauses-always-appended-in-order/316835#316835

We use `union all` because we don't need any of the deduplication logic
(`union` is really a union + distinct). `UNION ALL`` does preserve the
ordering of the operand queries but there is no actual gurantee that it
has this behavior in all scenarios so we need the extra `ORDER BY` at the
bottom.

See https://dba.stackexchange.com/questions/316818/are-results-from-union-all-clauses-always-appended-in-order/316835#316835

See #17293 (comment)

…the last event

Previously, it would use the event with the lowest `stream_ordering` that was
fetched (we want the highest `stream_ordering. `union` does not work how you
might think at first and does not preserve the ordering of the operand queries.

`union all` also doesn't necessarily have that gurantee but it does behave
that way. See https://dba.stackexchange.com/questions/316818/are-results-from-union-all-clauses-always-appended-in-order/316835#316835

We use `union all` because we don't need any of the deduplication logic
(`union` is really a union + distinct). `UNION ALL`` does preserve the
ordering of the operand queries but there is no actual gurantee that it
has this behavior in all scenarios so we need the extra `ORDER BY` at the
bottom.

See https://dba.stackexchange.com/questions/316818/are-results-from-union-all-clauses-always-appended-in-order/316835#316835

See #17293 (comment)

…event_in_room_before_stream_ordering

…before_stream_ordering' into madlittlemods/msc3575-sliding-sync-sort

Conflicts:
	synapse/storage/databases/main/stream.py
	tests/storage/test_stream.py

…t_last_event_in_room_before_stream_ordering(...)`

…ongside the sync rooms

…rship_snapshot_token.is_before_or_eq(to_token.room_key)`)

Wasn't caught in the tests because the test was wrong

Conflicts:
	synapse/storage/databases/main/stream.py
	tests/storage/test_stream.py

Conflicts:
	synapse/handlers/sliding_sync.py
	tests/handlers/test_sliding_sync.py

We always just sort by stream_ordering

> FWIW `stream_ordering` is unique, so we don't need a tie break.

See #17293 (comment)

See #17293 (comment)