akupchinskiy commented on PR #26201:
URL: https://github.com/apache/datafusion/pull/26201#issuecomment-6637180935
Another case this fixes: `DISTINCT ON` below a `UNION`. The rewrite makes
`a` nullable (`first_value` is always nullable) while the `Union` keeps the old
NOT NULL schema.
```sql
CREATE TABLE t (id BIGINT NOT NULL, a BIGINT NOT NULL, o BIGINT NOT NULL)
AS VALUES (1, 10, 1), (1, 11, 2), (2, 20, 1);
WITH d AS (SELECT DISTINCT ON (id) id, a FROM t ORDER BY id, o)
SELECT a FROM d UNION SELECT a FROM d;
```
On `main` (238ae32) it fails with `Internal error: Physical input schema
should be the same as the one converted from logical input schema. Differences:
field nullability at index 0 [a]: (physical) true vs (logical) false.`; on this
branch it returns `{10, 20}`. Might be worth a sqllogictest case, since it's
nullability rather than metadata.
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