shrivasshankar commented on code in PR #27148:
URL: https://github.com/apache/datafusion/pull/27148#discussion_r4516398469
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datafusion/physical-expr/src/expressions/cast.rs:
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@@ -699,6 +699,28 @@ fn can_propagate_cast_constraints(source: &DataType,
target: &DataType) -> bool
|| (source.is_integer() && target.is_integer())
// NaN bounds are unbounded; finite Float32 values widen exactly.
|| (*source == Float32 && *target == Float64)
+ || is_decimal_widening(source, target)
+}
+
+/// Whether a decimal-to-decimal cast keeps every value exactly, i.e. the
target
+/// has at least as many fractional and integer digits as the source. Casting
+/// bounds back to the source then rounds to a neighboring representable value,
+/// which never excludes a valid input.
+fn is_decimal_widening(source: &DataType, target: &DataType) -> bool {
Review Comment:
I moved it into a shared is_lossless_decimal_cast helper. i < 2.5 now
estimates 33.
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