apache/iceberg · error · UnsupportedOperationException

Wrong number of inputs (expected value)

Error message

Wrong number of inputs (expected value)

What it means

UnaryUnboundFunction is the shared base for single-argument Iceberg functions (days, hours, months, years). Before dispatching to doBind, its private valueType() checks that exactly one input was given and throws UnsupportedOperationException for any other argument count.

Solutions

1. Pass exactly one column: iceberg.days(col).
2. For multiple columns, apply the transform per column: days(a) and days(b) separately.
3. Inspect generated SQL to restore the missing argument.

Example fix

// before
SELECT iceberg.days(a, b) FROM t;
// after
SELECT iceberg.days(a), iceberg.days(b) FROM t;

-- unary functions take exactly 1 argument
SELECT iceberg.days(col) FROM t;

When it happens

Trigger: Calling iceberg.days() with zero arguments, or iceberg.months(col1, col2) with two or more — e.g. days() from templated SQL missing its parameter, or days(a, b) trying to bucket on two columns.

Common situations: Templated/generators omitting the argument; attempting multi-column transforms in one call (Iceberg requires one transform per column); copy-paste from binary functions like truncate().

Related errors

• Cannot bind: does not accept arguments
• Wrong number of inputs (expected width and value)
• Cannot bind: does not accept arguments
• Expected column to be date, tinyint, smallint, int, bigint…
• Expected number of buckets to be tinyint, shortint or int

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/4542d85f325b7589. Report an issue: GitHub.

Appendix: source

Thrown at spark/v4.0/spark/src/main/java/org/apache/iceberg/spark/functions/UnaryUnboundFunction.java:39

import org.apache.spark.sql.connector.catalog.functions.BoundFunction;
import org.apache.spark.sql.connector.catalog.functions.UnboundFunction;
import org.apache.spark.sql.types.DataType;
import org.apache.spark.sql.types.StructType;

/** An unbound function that accepts only one argument */
abstract class UnaryUnboundFunction implements UnboundFunction {

  @Override
  public BoundFunction bind(StructType inputType) {
    DataType valueType = valueType(inputType);
    return doBind(valueType);
  }

  protected abstract BoundFunction doBind(DataType valueType);

  private DataType valueType(StructType inputType) {
    if (inputType.size() != 1) {
      throw new UnsupportedOperationException("Wrong number of inputs (expected value)");
    }

    return inputType.fields()[0].dataType();
  }
}

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