alamb opened a new issue, #17589:
URL: https://github.com/apache/datafusion/issues/17589
### Is your feature request related to a problem or challenge?
One form of Case statements look like
```sql
CASE
WHEN <expr> THEN <expr>
WHEN <expr> THEN <expr>
...
ELSE
END
```
If there is a `WHEN true` then all subsequent case statements can not
execute. So for example
```sql
CASE
WHEN x=y THEN 1
WHEN true THEN 2
ELSE 3 -- can not be hit
END
```
Simplified to
```sql
CASE
WHEN x=y THEN 1
ELSE 2
END
```
And likewise
```sql
CASE
WHEN x=y THEN 1
WHEN y=z THEN 2
WHEN true THEN 3
WHEN a=b THEN 5 -- can not be hit
ELSE 5 -- can not be hit
END
```
Simplified to
```sql
CASE
WHEN x=y THEN 1
WHEN y=z THEN 2
ELSE 3
END
```
### Describe the solution you'd like
Implement the above simplifcation / optimization along with tests:
1. Unit tests in the simplifier
2. sqllogictests
### Describe alternatives you've considered
in https://github.com/apache/datafusion/pull/17450 @EeshanBembi implemented
one form of this simplification and I think it could be extended fairly
straightforwardly:
You can see this by running an explain plan (see that the name is changed to
`1`):
```sql
> explain select CASE WHEN true then 1 else 2 END;
+---------------+-------------------------------+
| plan_type | plan |
+---------------+-------------------------------+
| physical_plan | ┌───────────────────────────┐ |
| | │ ProjectionExec │ |
| | │ -------------------- │ |
| | │ CASE WHEN Boolean(true) │ |
| | │ THEN Int64(1) ELSE │ |
| | │ Int64(2) END: │ |
| | │ 1 │ |
| | └─────────────┬─────────────┘ |
| | ┌─────────────┴─────────────┐ |
| | │ PlaceholderRowExec │ |
| | └───────────────────────────┘ |
| | |
+---------------+-------------------------------+
1 row(s) fetched.
Elapsed 0.002 seconds.
```
However, it doesn't handle the case
### Additional context
_No response_
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