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.

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)
  {

View on GitHub (pinned to 9b90983fd2)

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));

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

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

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

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

• Not a numeric value type:
• Reverse lookup not allowed.
• Serialization not supported here
• Map column doesn't support getRow()
• Map column doesn't support lookupName()

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