databendlabs/databend · error

Unsupported column type for encoding

Error message

Unsupported column type for encoding

What it means

The sort row-encoding fixed-size visitor encodes columns into fixed-width sort keys. Its default visit_typed_column arm raises unimplemented!("Unsupported column type for encoding") for column types that cannot be represented as fixed-size rows. Sorting (ORDER BY / top-N) on such a column type via the fixed encoder is not supported.

Solutions

1. Cast the sort column to a supported comparable type (e.g. VARCHAR for variant, or sort by an extracted scalar)
2. Sort by a simpler expression/key (e.g. a numeric or string column) instead of the nested type
3. Upgrade Databend if the type is standard — encoder coverage grows over releases
4. Implement the missing type arm in the fixed encoder if you maintain the code, or route it to the variable encoder

Example fix

// before
SELECT * FROM t ORDER BY json_col;
// after
SELECT * FROM t ORDER BY json_col::string;

-- sql: verify sort keys are encoder-friendly scalar types
SELECT data_type FROM information_schema.columns
WHERE table_name = 't' AND column_name IN ('sort_col');
-- prefer Integer/Float/String/Date/Timestamp types for ORDER BY

fn sortable_fixed_type(ty: &DataType) -> bool {
    matches!(ty, DataType::Number(_) | DataType::String | DataType::Date
        | DataType::Timestamp | DataType::Boolean | DataType::Nullable(box inner)
        if matches!(**inner, DataType::Number(_) | DataType::String))
        || matches!(ty, DataType::Number(_) | DataType::String | DataType::Date | DataType::Timestamp | DataType::Boolean)
}

When it happens

Trigger: A query sorts by, or uses in a sort key, a column whose type the fixed-size row encoder lacks an arm for (e.g. complex/nested or large types that must use the variable encoder).

Common situations: ORDER BY on unusual types (arrays, maps, variants, bitmaps) reaching the fixed encoder; optimizer choosing fixed encoding for a newly added data type; window functions sorting over unsupported columns.

Related errors

• Unsupported column type for length calculation
• internal error: entered unreachable code
• {}
• Temp table id used up
• Invalid temp table desc

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/f5d590ae102bb654. Report an issue: GitHub.

Appendix: source

Thrown at src/query/pipeline/transforms/src/processors/transforms/sorts/core/row_convert/fixed.rs:460

    fn visit_interval(&mut self, buffer: Buffer<months_days_micros>) -> Result<()> {
        let buffer_bytes = buffer_to_bytes(self.buffer);
        fixed_encode(
            buffer_bytes,
            self.offsets,
            buffer,
            self.validity,
            self.field.asc,
            self.field.nulls_first,
        );
        Ok(())
    }

    fn visit_typed_column<T: ValueType>(
        &mut self,
        _column: T::Column,
        _data_type: &DataType,
    ) -> Result<()> {
        unimplemented!("Unsupported column type for encoding")
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use databend_common_expression::DataField;
    use databend_common_expression::DataSchemaRef;
    use databend_common_expression::DataSchemaRefExt;
    use databend_common_expression::SortColumnDescription;
    use databend_common_expression::SortField;
    use proptest::prelude::*;
    use proptest::strategy::Strategy;
    use proptest::strategy::ValueTree;
    use proptest::test_runner::TestRunner;

    use super::super::test_util::*;

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