apache/druid · error · UnsupportedOperationException

Column is not multi-valued

Error message

Column is not multi-valued

What it means

StringUtf8DictionaryEncodedColumn.getMultiValueRow() returns the multi-valued row (IndexedInts of dictionary ids) for a given row number. It throws UnsupportedOperationException when the underlying column does not have multiple values, because the multiValueColumn delegate does not exist in that case.

Solutions

  1. Check column.hasMultipleValues() (or ColumnCapabilities.hasMultipleValues()) before calling getMultiValueRow
  2. Use getSingleValueRow(int) for single-valued columns
  3. Ensure the ingestion spec keeps the column multi-valued (e.g. input is a JSON array) if multi-valued semantics are required

Example fix

// before
IndexedInts row = column.getMultiValueRow(rowNum);
// after
IndexedInts row = column.hasMultipleValues()
    ? column.getMultiValueRow(rowNum)
    : IndexibleInts.of(column.getSingleValueRow(rowNum));
Defensive patterns

Strategy: validation

Validate before calling

if (column.hasMultipleValues()) { row = column.getMultiValueRow(rowNum); } else { row = IndexibleInts.wrap(column.getSingleValueRow(rowNum)); }

Type guard

boolean isMultiValued(DimensionHandler h, ColumnCapabilities caps) { return caps != null && caps.hasMultipleValues(); }

Try / catch

try { return column.getMultiValueRow(rowNum); } catch (UnsupportedOperationException e) { return column.getSingleValueRowWrapped(rowNum); }

Prevention

When it happens

Trigger: Calling getMultiValueRow(rowNum) on a single-valued String column (one where hasMultipleValues() returns false), e.g. a column stored with plain single-value encoding.

Common situations: Generic query/segment code that assumes all string columns are multi-valued; schema changes that converted a column from multi-valued to single-valued; tests or tools written against multi-valued fixtures applied to single-valued segments.

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

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/0ecc33efca13c4e1. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/segment/column/StringUtf8DictionaryEncodedColumn.java:114

  }

  @Override
  public boolean hasMultipleValues()
  {
    return column == null;
  }

  @Override
  public int getSingleValueRow(int rowNum)
  {
    return column.get(rowNum);
  }

  @Override
  public IndexedInts getMultiValueRow(int rowNum)
  {
    if (!hasMultipleValues()) {
      throw new UnsupportedOperationException("Column is not multi-valued");
    }
    return multiValueColumn.get(rowNum);
  }

  @Override
  @Nullable
  public String lookupName(int id)
  {
    final ByteBuffer buffer = utf8Dictionary.get(id);
    if (buffer == null) {
      return null;
    }
    return StringUtils.fromUtf8(buffer);
  }

  @Override
  public int lookupId(String name)
  {

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