Jefffrey commented on code in PR #22482:
URL: https://github.com/apache/datafusion/pull/22482#discussion_r3314907985
##########
datafusion/functions/src/math/power.rs:
##########
@@ -369,34 +368,21 @@ fn pow_decimal256_float_fallback(
Ok(i256::from_i128(result_i128))
}
-/// Fallback implementation for decimal power when exponent is an array.
-/// Casts decimal to float64, computes power, and casts back to original
decimal type.
-/// This is used for performance when exponent varies per-row.
-fn pow_decimal_with_float_fallback(
- base: &ArrayRef,
+/// Compute `power(decimal_base, float_exponent)` by casting the base to
+/// `Float64` and running `pow` in float space; returns `Float64`.
+fn pow_decimal_via_float64(
Review Comment:
we could remove this entire codepath by letting signature coercion handle
the casting for us
https://github.com/apache/datafusion/blob/11a79a6217891cff67c8f963265f5673e6f63267/datafusion/functions/src/math/power.rs#L93-L100
- remove line 96, then we won't accept decimal + float, theyll be cast to
float + float and we can remove all the relevant code paths including this part
##########
datafusion/functions/src/math/power.rs:
##########
@@ -582,22 +490,43 @@ impl ScalarUDFImpl for PowerFunc {
)));
}
+ // The simplified expression must keep `return_type`'s declared
+ // type. For example, `power(decimal, float)` returns `Float64`,
+ // so rewriting `power(decimal, 0)` to `1::decimal` or
+ // `power(decimal, 1)` to the decimal base would violate that
+ // contract and trip the optimizer's schema-compatibility check.
+ // Wrap simplified forms in a cast to `return_type` when needed.
+ let return_type =
+ self.return_type(&[base_type.clone(), exponent_type.clone()])?;
+ let needs_cast = |t: &DataType| *t != return_type;
match exponent {
Expr::Literal(value, _)
if value == ScalarValue::new_zero(&exponent_type)? =>
{
Ok(ExprSimplifyResult::Simplified(lit(ScalarValue::new_one(
&base_type,
Review Comment:
instead of casting the result here we can replace `base_type` with
`return_type`
```rust
Ok(ExprSimplifyResult::Simplified(lit(ScalarValue::new_one(
&return_type,
)?)))
```
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