apache/iceberg · error · UnsupportedOperationException

Expected truncation col to be tinyint, shortint, int…

Error message

Expected truncation col to be tinyint, shortint, int, bigint, decimal, string, or binary

What it means

After validating the width, TruncateFunction.bind() dispatches on the value column's type to a typed implementation. Only tinyint, smallint, int, bigint, decimal, string, and binary are supported; other types (timestamp, date, double, float, boolean, complex types) are rejected with this UnsupportedOperationException.

Solutions

1. For temporal columns, use the appropriate transform instead: iceberg.days(ts), iceberg.hours(ts), or iceberg.months(ts).
2. For floats/doubles, cast to DECIMAL: truncate(cast(x AS DECIMAL(38, 4)) width-adjusted).
3. For other cases cast to a supported type, e.g. CAST(col AS STRING) before truncating.
4. Verify the value column type with typeof(col).

Example fix

// before
SELECT iceberg.truncate(10, event_ts) FROM t; -- TIMESTAMP not supported
// after
SELECT iceberg.days(event_ts) FROM t;
-- or, for numeric
SELECT iceberg.truncate(4, CAST(score AS DECIMAL(38, 4))) FROM t;

val t = col.dataType
val supported = Seq(ByteType, ShortType, IntegerType, LongType, StringType, BinaryType)
require(supported.contains(t) || t.isInstanceOf[DecimalType], s"truncate value type $t unsupported")

def isTruncatable(t: DataType): Boolean = t match {
  case _: DecimalType => true
  case ByteType | ShortType | IntegerType | LongType | StringType | BinaryType => true
  case _ => false
}

When it happens

Trigger: Calling iceberg.truncate(width, col) where col is TIMESTAMP, DATE, DOUBLE, FLOAT, BOOLEAN, ARRAY, STRUCT, or MAP — e.g. truncate(10, event_ts).

Common situations: Trying to truncate a timestamp column (use the days/hours/months transforms instead); truncating float/double measurements; passing nested-typed columns.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Expected column to be date, tinyint, smallint, int, bigint…
• Expected value to be date or timestamp
• Expected value to be date or timestamp
• Expected value to be timestamp
• Cannot bind: does not accept arguments

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/d8d95deaeef34a8a. Report an issue: GitHub.

Appendix: source

Thrown at spark/v4.0/spark/src/main/java/org/apache/iceberg/spark/functions/TruncateFunction.java:93

    DataType valueType = valueField.dataType();
    if (valueType instanceof ByteType) {
      return new TruncateTinyInt();
    } else if (valueType instanceof ShortType) {
      return new TruncateSmallInt();
    } else if (valueType instanceof IntegerType) {
      return new TruncateInt();
    } else if (valueType instanceof LongType) {
      return new TruncateBigInt();
    } else if (valueType instanceof DecimalType) {
      return new TruncateDecimal(
          ((DecimalType) valueType).precision(), ((DecimalType) valueType).scale());
    } else if (valueType instanceof StringType) {
      return new TruncateString();
    } else if (valueType instanceof BinaryType) {
      return new TruncateBinary();
    } else {
      throw new UnsupportedOperationException(
          "Expected truncation col to be tinyint, shortint, int, bigint, decimal, string, or binary");
    }
  }

  @Override
  public String description() {
    return name()
        + "(width, col) - Call Iceberg's truncate transform\n"
        + "  width :: width for truncation, e.g. truncate(10, 255) -> 250 (must be an integer)\n"
        + "  col :: column to truncate (must be an integer, decimal, string, or binary)";
  }

  @Override
  public String name() {
    return "truncate";
  }

  public abstract static class TruncateBase<T> extends BaseScalarFunction<T> {

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