pepijnve commented on PR #17813:
URL: https://github.com/apache/datafusion/pull/17813#issuecomment-3514121797
In 427fc30fed1bfdfd49f5098a3e1ba955e5452704 I've added an SLT that
illustrates how better nullability reporting may allow optimisation of certain
queries. It's a contrived query, but it's just a test
The query
```
SELECT CASE WHEN CASE WHEN a IS NOT NULL THEN a ELSE 1 END IS NOT NULL THEN
a ELSE 1 END FROM (
VALUES (10), (20), (30)
) t(a)
```
get squashed down to
```
ProjectionExec: expr=[column1@0 as CASE WHEN CASE WHEN t.a IS NOT NULL THEN
t.a ELSE Int64(1) END IS NOT NULL THEN t.a ELSE Int64(1) END]
```
while current `main` will evaluate this as
```
ProjectionExec: expr=[CASE WHEN CASE WHEN column1@0 IS NOT NULL THEN
column1@0 ELSE 1 END IS NOT NULL THEN column1@0 ELSE 1 END as CASE WHEN CASE
WHEN t.a IS NOT NULL THEN t.a ELSE Int64(1) END IS NOT NULL THEN t.a ELSE
Int64(1) END]
```
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