joe-clickhouse commented on PR #43960:
URL: https://github.com/apache/superset/pull/43960#issuecomment-5590793148

   From the ClickHouse and clickhouse-connect side, it does look like this 
change correctly preserves explicit UTC offsets. `DateTime64(3, 'Asia/Tehran')` 
now returns a timezone-aware datetime, and its ISO string is 
`2026-01-15T12:30:00.123000+03:30` which is 09:00 UTC. The old code replaces 
the offset with `Z`, which changes the instant.
   
   I also tested Superset 4.1.1 and 6.1.0 against ClickHouse 26.6 with 
clickhouse-connect 1.8.0. Every chart data mode I tried returned this column as 
an epoch number, and `normalizeTimestamp` only handles strings, so this change 
appears to never even touch those values. SQL Lab returned the ISO string with 
the offset, but its results grid does not run it through `normalizeTimestamp` 
either.
   
   I then had some agents do some digging and they think that the reporter's 
display change comes from #37979, which corrected the backend epoch conversion. 
So for this Tehran value, 4.1.1 returned the epoch for `12:30Z` and 6.1.0 
returns the epoch for `09:00Z`. The old value happened to read as the 
column-local time under the default UTC formatter, but it was the wrong instant.
   
   This PR makes the same correction for frontend strings, which is right, but 
I don't think it'll change what the reporter's chart shows. That request needs 
a way to choose a display timezone. Master already has a dataset timezone 
setting from #37014, but it currently raises on timezone-aware columns like 
this one. (Probably worth filing separately). All that said, it might not be 
correct to say  `Fixes #43927` here instead just yet.
   
   For regression coverage here though, I would add fractional seconds and 
assert the parsed epoch. A DST fall-back pair with identical wall times but 
`-04:00` and `-05:00` offsets would also help becuase in testing I saw that the 
old normalizer collapsed those two instants into one but this PR keeps them an 
hour apart.
   
   Hope that helps!


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