adriangb commented on code in PR #23844:
URL: https://github.com/apache/datafusion/pull/23844#discussion_r3640993613
##########
datafusion/physical-expr/src/expressions/case.rs:
##########
@@ -1537,6 +1543,25 @@ fn replace_with_null(
Ok(with_null)
}
+/// Returns the innermost [`PhysicalExpr`] that is provably null if `expr` is
null.
+///
+/// Keep this in sync with the logical-plan equivalent,
`unwrap_certainly_null_expr`
+/// in `datafusion/expr/src/expr_schema.rs`. If the two disagree on which
wrappers
+/// are null-preserving, `CASE` nullability computed by the logical and
physical
+/// planners can diverge and cause a schema mismatch during planning (the bug
this
+/// PR fixes).
Review Comment:
```suggestion
/// planners can diverge and cause a schema mismatch during planning.
/// See https://github.com/apache/datafusion/pull/23844 for rationale.
```
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