neilconway opened a new issue, #26024:
URL: https://github.com/apache/datafusion/issues/26024
### Describe the bug
The result of `nvl2(x, a, b)` should depend only on `a` and `b`; `x` is only
checked for NULL. The type of `x` currently changes the result type, and some
combinations fail:
- Decimal results are widened to a larger precision and scale, or turned
into strings.
- Timestamp results fail to plan when `x` is an integer, and fail during
optimization when `x` is a string literal.
The equivalent `CASE WHEN x IS NOT NULL THEN a ELSE b END` works in every
case.
### To Reproduce
```sql
CREATE TABLE t AS SELECT
1 AS i, 1.5 AS f, 'a' AS s,
CAST(1.23 AS DECIMAL(5,2)) AS d1, CAST(4.56 AS DECIMAL(5,2)) AS d2,
TIMESTAMP '2024-01-01 10:00:00' AS ts1, TIMESTAMP '2024-01-02 10:00:00' AS
ts2;
SELECT arrow_typeof(CASE WHEN i IS NOT NULL THEN d1 ELSE d2 END) AS
case_type FROM t;
-- Decimal128(5, 2)
SELECT nvl2(i, d1, d2) AS v, arrow_typeof(nvl2(i, d1, d2)) AS v_type FROM t;
-- 1.23 | Decimal128(22, 2)
SELECT nvl2(f, d1, d2) AS v, arrow_typeof(nvl2(f, d1, d2)) AS v_type FROM t;
-- 1.230000000000000 | Decimal128(30, 15)
SELECT nvl2(s, d1, d2) AS v, arrow_typeof(nvl2(s, d1, d2)) AS v_type FROM t;
-- 1.23 | Utf8
SELECT nvl2(i, ts1, ts2) AS v FROM t;
-- Error during planning: Execution error: Function 'nvl2' user-defined
coercion failed with: Internal error: Coercion from Int64 to Timestamp(ns)
failed..
SELECT nvl2('a', ts1, ts2) AS v FROM t;
-- Optimizer rule 'simplify_expressions' failed
-- caused by
-- Failed to cast field 'lit' from Utf8 to Timestamp(ns)
-- caused by
-- Arrow error: Parser error: Error parsing timestamp from 'a': timestamp
must contain at least 10 characters
```
### Expected behavior
`nvl2` returns the same results as the equivalent `CASE` expression:
- The three decimal queries return `1.23` as `Decimal128(5, 2)`.
- The two timestamp queries return `2024-01-01T10:00:00`.
### Additional context
Reproduced on `main` at commit 2b1fcae86, in both release and debug builds.
*This bug report was generated by Claude.*
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