alamb opened a new issue #1609:
URL: https://github.com/apache/arrow-datafusion/issues/1609
As we found on #1601, the return type of a `CASE` statement is currently
based on the `THEN` clause. One problem with this this logic is that it may
cause a cast (e.g. `float64` to `int`) that loses accuracy.
The goal of this ticket would be to compute the return type of a case
statement by applying coercion rules to the various clauses.
@xudong963 found that Postgres' behavior is reasonable:
```sql
postgres=# SELECT * FROM test;
a
---
1
2
3
(3 rows)
postgres=# SELECT a,
CASE WHEN a=1 THEN 1.2
ELSE 0
END
FROM test;
a | case
---+------
1 | 1.2
2 | 0
3 | 0
(3 rows)
postgres=# SELECT a,
CASE WHEN a=1 THEN 12
ELSE 5.4
END
FROM test;
a | case
---+------
1 | 12
2 | 5.4
3 | 5.4
(3 rows)
```
_Originally posted by @xudong963 in
https://github.com/apache/arrow-datafusion/issues/1601#issuecomment-1015046138_
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