apache/iceberg · error · UnsupportedOperationException

Cannot apply unknown modify-column-position change: {modifyC

Error message

Cannot apply unknown modify-column-position change: {modifyColumnPosition}

What it means

applyModifyColumnPosition supports only TableChange.First and TableChange.After. Any other ModifyColumnPosition subtype (or null beyond these) throws UnsupportedOperationException, because Iceberg moves only support first/after semantics.

Source

Thrown at flink/v2.1/flink/src/main/java/org/apache/iceberg/flink/util/FlinkAlterTableUtil.java:241

          (TableChange.ModifyColumnComment) modifyColumn;
      pendingUpdate.updateColumnDoc(
          modifyComment.getOldColumn().getName(), modifyComment.getNewComment());
    } else {
      throw new UnsupportedOperationException(
          "Cannot apply unknown modify-column change: " + modifyColumn);
    }
  }

  private static void applyModifyColumnPosition(
      UpdateSchema pendingUpdate, TableChange.ModifyColumnPosition modifyColumnPosition) {
    TableChange.ColumnPosition newPosition = modifyColumnPosition.getNewPosition();
    if (newPosition instanceof TableChange.First) {
      pendingUpdate.moveFirst(modifyColumnPosition.getOldColumn().getName());
    } else if (newPosition instanceof TableChange.After) {
      TableChange.After after = (TableChange.After) newPosition;
      pendingUpdate.moveAfter(modifyColumnPosition.getOldColumn().getName(), after.column());
    } else {
      throw new UnsupportedOperationException(
          "Cannot apply unknown modify-column-position change: " + modifyColumnPosition);
    }
  }

  private static void applyUniqueConstraint(
      UpdateSchema pendingUpdate, UniqueConstraint constraint) {
    switch (constraint.getType()) {
      case PRIMARY_KEY:
        pendingUpdate.setIdentifierFields(constraint.getColumns());
        break;
      case UNIQUE_KEY:
        throw new UnsupportedOperationException(
            "Unsupported table change: setting unique key constraints.");
      default:
        throw new UnsupportedOperationException(
            "Cannot apply unknown unique constraint: " + constraint.getType().name());
    }
  }

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Convert the position change to TableChange.After with the preceding column name, or First
2. Implement a Before->After translation (after the previous column) before calling the util
3. Drop the positional clause from the DDL for Iceberg tables

Example fix

// before
TableChange.Before before = ...; applyModifyColumnPosition(update, new ModifyColumnPosition(col, before));
// after
TableChange.After after = TableChange.after(previousColumnName());
applyModifyColumnPosition(update, new TableChange.ModifyColumnPosition(col, after));

if (newPosition instanceof TableChange.First) {
  // ok
} else if (newPosition instanceof TableChange.After a) {
  if (a.column() == null) throw new IllegalArgumentException("After.column must be set");
} else {
  throw new IllegalArgumentException("Unsupported column position: " + newPosition);
}

boolean isSupportedPosition(TableChange.ColumnPosition p) {
  return p instanceof TableChange.First || p instanceof TableChange.After;
}

try {
  FlinkAlterTableUtil.applySchemaChanges(update, List.of(change));
} catch (UnsupportedOperationException e) {
  if (e.getMessage().contains("modify-column-position")) { /* translate to After/First */ }
  throw e;
}

When it happens

Trigger: Passing a TableChange.ModifyColumnPosition whose newPosition is neither First nor After (e.g. TableChange.Before-like custom subtype) through applyAddColumn/applyModifyColumn.

Common situations: Custom Flink catalog or SQL dialect emitting positional change types Iceberg cannot express.

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 table change: AddWatermark.
• Unsupported table change: ModifyWatermark.
• Unsupported table change: DropWatermark.
• Unsupported table change: DropConstraint.
• Cannot apply unknown table change: {change}

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/d79231bc9287a93f. Report an issue: GitHub.