cecemei commented on code in PR #18403:
URL: https://github.com/apache/druid/pull/18403#discussion_r2335310625
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processing/src/main/java/org/apache/druid/data/input/impl/AggregateProjectionSpec.java:
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@@ -218,10 +223,9 @@ private static ProjectionOrdering
computeOrdering(VirtualColumns virtualColumns,
String timeColumnName = null;
Granularity granularity = null;
- // try to find the __time column equivalent, which might be a time_floor
expression to model granularity
- // bucketing. The time column is decided as the finest granularity on
__time detected. If the projection does
- // not have a time-like column, the granularity will be handled as ALL for
the projection and all projection
- // rows will use a synthetic timestamp of the minimum timestamp of the
incremental index
+
+ // determine the granularity and time column name for the projection,
based on the first time-like grouping column.
+ // if there are multiple time-like grouping columns, they must be
"coarser" than the first time-like grouping column.
Review Comment:
`finer` is not completely safe, we're looking for the most compatible gran,
e.x. between `PT2H` and `PT3H`, we can find `PT1H` as compatible (but this is
not currently supported, i'm just using this as an example).
and deciding on the most compatible is tricky since we don't want non-UTC
time to sneak in, e.x. `PT30M` in Pacific time would sort of invalidate our
`PT1H` gran in UTC, handling this just makes things more complicated, thus
choose to handle in a strict way here
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