apache/druid · error · ExpressionValidationException

needs a LONG as its second argument but got %s instead

Error message

needs a LONG as its second argument but got %s instead

What it means

Thrown when HUMAN_READABLE_BYTES_FORMAT's optional second argument (precision) is present but not of type LONG. Precision must be an integer in [0,3]; STRING, DOUBLE, or other types are rejected with this message.

Source

Thrown at processing/src/main/java/org/apache/druid/math/expr/Function.java:4693

       */
      if (valueParam.value() != null && !valueParam.type().anyOf(ExprType.LONG, ExprType.DOUBLE)) {
        throw validationFailed(
            "needs a number as its first argument but got %s instead",
            valueParam.type()
        );
      }

      /**
       * By default, precision is 2
       */
      long precision = 2;
      if (args.size() > 1) {
        ExprEval precisionParam = args.get(1).eval(bindings);
        if (precisionParam.value() == null) {
          throw validationFailed("needs a LONG as its second argument but got null");
        }
        if (!precisionParam.type().is(ExprType.LONG)) {
          throw validationFailed("needs a LONG as its second argument but got %s instead", precisionParam.type());
        }
        precision = precisionParam.asLong();
        if (precision < 0 || precision > 3) {
          throw validationFailed("given precision[%d] must be in the range of [0,3]", precision);
        }
      }

      return ExprEval.ofString(HumanReadableBytes.format(valueParam.asLong(), precision, this.getUnitSystem()));
    }

    @Override
    public void validateArguments(List<Expr> args)
    {
      validationHelperCheckAnyOfArgumentCount(args, 1, 2);
    }

    @Nullable
    @Override

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Pass an integer literal: human_readable_bytes_format(b, 2).
2. Cast the argument: CAST(prec AS BIGINT).
3. Change the datasource/schema so the precision column is BIGINT.
4. Remove the argument to accept the default precision of 2.

Example fix

// before
human_readable_bytes_format(b, '2')
// after
human_readable_bytes_format(b, 2)

CAST(precision_expr AS BIGINT) -- ensure integer type

if (!(p instanceof Integer || p instanceof Long)) throw new IllegalArgumentException("precision must be a LONG");

When it happens

Trigger: Calling human_readable_bytes_format(value, '2') with a string precision, or a DOUBLE column/literal like 2.0 as the second argument.

Common situations: Clients sending precision as a JSON string; columns typed as DOUBLE or VARCHAR in the datasource; confusion with languages where 2.0 is a valid int.

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

• needs a number as its first argument but got %s instead
• Cannot implicitly cast [%s] to [%s]
• first argument must be constant STRING expression containing
• second argument must be a base64 encoded STRING value but go
• Cannot cast [%s] to [%s] (Types.InvalidCastException from in

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/e579e7e82c7d721f. Report an issue: GitHub.