apache/druid · error · ExpressionValidationException

requires 1 argument

Error message

requires 1 argument

What it means

Druid's expression function validation throws this when a NamedFunction implementation that expects exactly one argument receives a different number of arguments. The validationHelperCheckArgumentCount helper on NamedFunction compares args.size() against the declared count and throws validationFailed. It is thrown at query parsing/planning time, before evaluation.

Source

Thrown at processing/src/main/java/org/apache/druid/math/expr/NamedFunction.java:73

  {
    throw new ExpressionProcessingException(this, reasonFormat, args);
  }

  default ExpressionProcessingException processingFailed(Throwable e, String reasonFormat, Object... args)
  {
    throw new ExpressionProcessingException(this, e, reasonFormat, args);
  }

  /**
   * Helper method for implementors performing validation to check if the argument count is expected
   */
  default void validationHelperCheckArgumentCount(List<Expr> args, int count)
  {
    if (args.size() != count) {
      if (count == 0) {
        throw validationFailed("does not accept arguments");
      } else if (count == 1) {
        throw validationFailed("requires 1 argument");
      }
      throw validationFailed("requires %d arguments", count);
    }
  }

  /**
   * Helper method for implementors performing validation to check if there are at least as many arguments as specified
   */
  default void validationHelperCheckMinArgumentCount(List<Expr> args, int count)
  {
    if (args.size() < count) {
      if (count == 1) {
        throw validationFailed("requires at least 1 argument");
      }
      throw validationFailed("requires at least %d arguments", count);
    }
  }

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Count the arguments passed to the function and pass exactly one
2. Check the function's validation in its NamedFunction implementation to confirm expected arity
3. If a two-argument form is intended, use a function variant that supports it (e.g. a function accepting a range of counts)

Example fix

// before
long_value = ceil()
// after
long_value = ceil(value_expr)

if (args.size() != 1) { throw new IllegalArgumentException(funcName + " requires exactly 1 argument, got " + args.size()); }

boolean isSingleArg(List<Expr> args) { return args != null && args.size() == 1; }

try { expr = Parser.parse(exprString); } catch (ExpressionValidationException e) { log.error("Bad expression arity: %s", e.getMessage()); throw new QueryPlanningException(e); }

When it happens

Trigger: Calling an expression function that declares validationHelperCheckArgumentCount(args, 1) with 0 arguments (e.g. a single-argument function like CEIL invoked as CEIL()) or with 2+ arguments (e.g. CEIL(x, y)).

Common situations: Typos in SQL/native expressions, copy-pasted expressions with leftover arguments, dynamic expression builders concatenating extra operands, or SQL dialect translations producing wrong arity.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• requires %d arguments
• requires at least 1 argument
• requires at least %d arguments
• requires %d to %d arguments
• requires %s arguments

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/667795bcea83d9ce. Report an issue: GitHub.