apache/druid · error · java.lang.UnsupportedOperationException

attempt to get double[] from string[] only scalar binding

Error message

attempt to get double[] from string[] only scalar binding

What it means

Same string-only binding limitation, for double[]: the deferred-evaluation vector bindings for a single string input cannot produce double vectors, so getDoubleVector throws UnsupportedOperationException by design rather than returning wrong data.

Solutions

Cast the string input to DOUBLE explicitly in the expression so the proper typed selector/binding is used
Use string-safe functions or numeric parse functions that operate on strings
Disable vectorization if the expression typing cannot be adjusted

Example fix

// before
double_func(string_col)
// after
CAST(string_col AS DOUBLE) -- then apply double_func

Defensive patterns

Strategy: try-catch

Validate before calling

// ensure expression only uses string-compatible functions over the string input binding
Expr.InputBindingTypes t = expr.analyzeInputs();
if (!t.getRequiredBindings().isEmpty() && !isStringTyped(expr)) { /* replan */ }

Try / catch

try {
  return bindings.getDoubleVector(name);
} catch (UnsupportedOperationException e) {
  return evalAsDouble(bindings.getStringVector(name)); // or disable vectorization
}

Prevention

CAST strings to DOUBLE before double arithmetic in vectorized expressions
Keep single-input deferred selectors paired with string-typed expressions
Cover vectorized type-mixing queries in regression tests

When it happens

Trigger: Expression evaluation requests getDoubleVector(name) from the single-string-input binding, typically when an expression over a string column is vector-typed as double[].

Common situations: Expressions applying double math directly to string inputs under vectorization; planner typing mismatches after expression changes.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/35a712238fdb0b74. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/segment/virtual/SingleStringInputDeferredEvaluationExpressionDimensionVectorSelector.java:164

      return -1;
    }

    @Override
    public Object[] getObjectVector(String name)
    {
      return currentValue;
    }

    @Override
    public long[] getLongVector(String name)
    {
      throw new UnsupportedOperationException("attempt to get long[] from string[] only scalar binding");
    }

    @Override
    public double[] getDoubleVector(String name)
    {
      throw new UnsupportedOperationException("attempt to get double[] from string[] only scalar binding");
    }

    @Nullable
    @Override
    public boolean[] getNullVector(String name)
    {
      throw new UnsupportedOperationException("attempt to get boolean[] null vector from string[] only scalar binding");
    }
  }
}

View on GitHub (pinned to 9b90983fd2)