jayzhan211 commented on code in PR #26452:
URL: https://github.com/apache/datafusion/pull/26452#discussion_r4434159595
##########
datafusion/pruning/src/pruning_predicate.rs:
##########
@@ -1349,6 +1349,16 @@ fn verify_support_type_for_prune(from_type: &DataType,
to_type: &DataType) -> Re
}
_ => to_type,
};
+ // Casting a timestamp to a time-of-day wraps at midnight and does not
+ // preserve ordering across day boundaries. Casting timestamp min/max
+ // statistics could therefore produce invalid bounds and prune matches.
Review Comment:
@rgbuilds thanks for the fix! The root cause is that pruning has its own
order check that allows any cast unless exactly one side is a string, instead
of asking `is_order_preserving_cast` in
`physical-expr/src/expressions/cast.rs`, which already rejects this cast. So
similar casts still drop rows here, e.g. `CAST(i AS BOOLEAN)` and `CAST(i AS
BYTEA)` (#26981). #26982 moves pruning onto that shared rule and will replace
this arm, so this is fine to merge as the fix for #26451. Could you add a TODO
here so nobody extends this special case in the meantime?
```suggestion
// Casting a timestamp to a time-of-day wraps at midnight and does not
// preserve ordering across day boundaries. Casting timestamp min/max
// statistics could therefore produce invalid bounds and prune matches.
// TODO: decide this with `is_order_preserving_cast` (physical-expr),
which
// already rejects this cast, instead of special-casing pairs here.
```
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