influxdata/influxdb · error

Expected scalar value

Error message

Expected scalar value

What it means

Panic in the scalar_value_passthrough test of date_bin_wallclock: the date_bin wallclock UDF is documented/expected to return a ColumnarValue::Scalar when given scalar inputs, so any other variant (ColumnarValue::Array) is a contract violation and the test panics.

Solutions

1. Ensure the UDF's invoke has a scalar fast-path that returns ColumnarValue::Scalar when all inputs are scalars
2. Check the interval argument is a ScalarValue and not accidentally converted to an array upstream
3. Compare against the DataFusion version's ColumnarValue semantics for scalar UDFs
4. If behavior is intentionally array-only, update the test expectation rather than the function

Example fix

// before (UDF invoke)
ColumnarValue::Array(...)  // always array
// after
if args.iter().all(|a| matches!(a, ColumnarValue::Scalar(_))) {
    ColumnarValue::Scalar(ScalarValue::TimestampNanosecond(Some(binned), tz.clone()))
} else {
    ColumnarValue::Array(...)
}

// Rust: verify UDF returns scalar for scalar-only args before unwrapping
fn returns_scalar(v: &ColumnarValue) -> bool { matches!(v, ColumnarValue::Scalar(_)) }

fn expect_scalar(v: ColumnarValue) -> Option<ScalarValue> {
    match v { ColumnarValue::Scalar(s) => Some(s), _ => None }
}

let scalar = match result {
    ColumnarValue::Scalar(s) => s,
    other => panic!("Expected scalar value, got: {other:?}"),
};

When it happens

Trigger: Calling date_bin_wallclock's invoke with scalar timestamp and interval arguments and receiving ColumnarValue::Array instead of ColumnarValue::Scalar — i.e. the function implementation stopped special-casing scalar inputs.

Common situations: Refactoring the UDF's invoke to always return arrays; a DataFusion ScalarUDF trait version change altering how scalar-only calls are represented; forgetting the scalar fast-path after adding timezone support.

Related errors

• Error computing AND
• Unexpected err evaluating
• datafusion error
• error while executing plan
• Expected array value

AI-assisted analysis of influxdata/influxdb@06200ef96b (2026-09-19). Data as JSON: /api/errors/daa6c1fa0986172b. Report an issue: GitHub.

Appendix: source

Thrown at core/query_functions/src/date_bin_wallclock.rs:556

            ))),
            ColumnarValue::Scalar(ScalarValue::TimestampNanosecond(
                Some(MAYDAY + 60 * 60 * 1_000_000_000),
                None,
            )),
        ];
        let arg_fields = arg_to_fields(&args);
        let result = match udf
            .invoke_with_args(ScalarFunctionArgs {
                args,
                arg_fields,
                number_rows: 13,
                return_field: return_field(DataType::Timestamp(TimeUnit::Nanosecond, None)),
                config_options: default_config_options(),
            })
            .unwrap()
        {
            ColumnarValue::Scalar(scalar) => scalar,
            _ => panic!("Expected scalar value"),
        };
        assert_eq!(result, ScalarValue::TimestampNanosecond(Some(MAYDAY), None),);
    }

    #[test]
    fn scalar_value_with_timezone() {
        let udf = DateBinWallclockUDF::default();
        let tz = Arc::from("America/New_York");
        let args = vec![
            ColumnarValue::Scalar(ScalarValue::IntervalMonthDayNano(Some(
                IntervalMonthDayNano::new(0, 1, 0),
            ))),
            ColumnarValue::Scalar(ScalarValue::TimestampNanosecond(
                Some(MAYDAY + 60 * 60 * 1_000_000_000),
                Some(Arc::clone(&tz)),
            )),
        ];
        let arg_fields = arg_to_fields(&args);

View on GitHub (pinned to 06200ef96b)