databendlabs/databend · error

Unsupported column type for encoding

Error message

Unsupported column type for encoding

What it means

This is a catch-all panic in the sort-row encoding visitor: `visit_typed_column` is the default visitor method that every concrete ValueType must override. It is hit when the encoding logic encounters a column type whose ValueType visitor did not implement typed-column conversion, so the framework aborts with `unimplemented!` instead of silently producing wrong sort keys.

Solutions

1. Check which data type the failing query sorts on and confirm whether its ValueType visitor implements visit_typed_column in src/query/pipeline/transforms/src/processors/transforms/sorts/core/row_convert/
2. Implement visit_typed_column for that ValueType, encoding the column into the variable-length sort row
3. Work around in SQL by casting the column to a supported sortable type (e.g. CAST(variant_col AS VARCHAR)) before ORDER BY
4. File a Databend issue with the query and data type if the type should be supported

Example fix

// before (visitor for MyType falls through to default)
// ... no visit_typed_column impl ...
// after
fn visit_typed_column(&mut self, column: MyTypeColumn, data_type: &DataType) -> Result<()> {
    self.builder.push(my_type_sort_key(column), data_type)
}

const SORTABLE_ENCODABLE_TYPES = ["Nullable","String","Number","Date","Timestamp","Decimal"];
function isSortEncodable(colType) {
  return SORTABLE_ENCODABLE_TYPES.some(t => colType.startsWith(t)) ||
         !/^(variant|map|array|tuple|geography|geometry)$/i.test(colType.replace(/^nullable\((.*)\)$/, "$1"));
}
if (!isSortEncodable(column.dataType)) {
  column.query = `CAST(${column.name} AS VARCHAR)`;
}

function isVariantLike(dataType) {
  const base = dataType.replace(/^Nullable\((.*)\)$/, "$1").toLowerCase();
  return ["variant","map","object"].includes(base);
}

When it happens

Trigger: Sorting (ORDER BY / top-k) over a column whose data type's ValueType<T> does not override `visit_typed_column` in `row_convert/variable.rs`, e.g. a newly added or unusual type (map, variant, exotic nested types) reaching the variable-length row encoder.

Common situations: Running ORDER BY on an exotic column type (e.g. VARIANT, MAP, or a newly supported type) that the sort key encoder hasn't been extended for; adding a new data type in the query engine without updating the sort row converters.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Unsupported column type for encoding
• Unsupported column type for length calculation
• Unsupported format for
• Unsupported source type. Expected path, pandas.DataFrame…
• Access denied: is outside allowed directories

AI-assisted analysis of databendlabs/databend@288d84d76e (2026-09-11). Data as JSON: /api/errors/2f3bf2eefa3a2d46. Report an issue: GitHub.

Appendix: source

Thrown at src/query/pipeline/transforms/src/processors/transforms/sorts/core/row_convert/variable.rs:798

    }

    fn visit_variant(&mut self, column: BinaryColumn) -> Result<()> {
        var_encode(
            self.out,
            column.iter(),
            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 databend_common_base::base::OrderedFloat;
    use databend_common_expression::Column;
    use databend_common_expression::DataField;
    use databend_common_expression::DataSchemaRefExt;
    use databend_common_expression::FromData;
    use databend_common_expression::SortColumnDescription;
    use databend_common_expression::SortField;
    use databend_common_expression::types::*;
    use jsonb::OwnedJsonb;
    use proptest::prelude::*;
    use proptest::strategy::ValueTree;
    use proptest::test_runner::TestRunner;

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