apache/druid · error · ExpressionValidationException

requires at least 1 argument

Error message

requires at least 1 argument

What it means

Generic argument-count guard used by Druid's named expression functions: validationHelperCheckMinArgumentCount(args, 1) fires when a SQL/Druid expression function that requires at least one argument (e.g. a string, arithmetic, or aggregation helper function) is invoked with zero arguments. It is a sentinel message from a shared validation helper, not function-specific logic; the fix is to supply the required argument(s) at the call site, e.g. CHANGE to CONCAT(x, ...) instead of empty parentheses.

Solutions

1. Pass at least one argument
2. Guard the call site: skip the function entirely when the operand list is empty
3. Check the function's validation to confirm the minimum

Example fix

// before
expr = concat()
// after
expr = concat(a, b)

if (args.isEmpty()) { throw new IllegalArgumentException(funcName + " requires at least 1 argument"); }

boolean hasMinArity(List<Expr> args, int min) { return args != null && args.size() >= min; }

try { expr = Parser.parse(exprString); } catch (ExpressionValidationException e) { // handle empty-argument expressions by substituting a default }

When it happens

Trigger: Invoking a variadic-or-minimum function such as GREATEST, CONCAT, or array functions with an empty argument list.

Common situations: Building expressions programmatically with an empty operand list; SQL like CONCAT() generated from zero folded inputs.

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

• must have an even number of arguments
• requires 1 argument
• requires at least arguments
• requires arguments
• requires to arguments

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/c9fc41e665e88584. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/math/expr/NamedFunction.java:86

  {
    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);
    }
  }

  default void validationHelperCheckArgumentRange(List<Expr> args, int start, int end)
  {
    if (args.size() < start || args.size() > end) {
      throw validationFailed("requires %d to %d arguments", start, end);
    }
  }

  /**
   * Helper method for implementors performing validation to check if argument count is any of specified counts
   */
  default void validationHelperCheckAnyOfArgumentCount(List<Expr> args, int... counts)
  {
    boolean satisfied = false;

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