joroKr21 commented on code in PR #12965:
URL: https://github.com/apache/datafusion/pull/12965#discussion_r1802959651
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datafusion/physical-expr/src/scalar_function.rs:
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@@ -147,8 +149,19 @@ impl PhysicalExpr for ScalarFunctionExpr {
if let ColumnarValue::Array(array) = &output {
if array.len() != batch.num_rows() {
- return internal_err!("UDF returned a different number of rows
than expected. Expected: {}, Got: {}",
- batch.num_rows(), array.len());
+ // If the function is not volatile and all arguments are
scalars,
+ // we can assume that returning a one-element array is
equivalent to returning a scalar.
+ let preserve_scalar = array.len() == 1
+ && self.fun.signature().volatility != Volatility::Volatile
Review Comment:
A volatile function is supposed to return a different result on every
invocation so I don't think it's safe to do that. The example we were
discussing in the earlier PR is a hypothetical `rand(upper_bound: Int64) ->
Int64` function.
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