@Override
  public VectorExpressionDescriptor.Descriptor getDescriptor() {
    return (new VectorExpressionDescriptor.Builder())
        .setMode(
            VectorExpressionDescriptor.Mode.PROJECTION)
        .setNumArguments(2)
        .setArgumentTypes(
            VectorExpressionDescriptor.ArgumentType.STRING_FAMILY,
            VectorExpressionDescriptor.ArgumentType.STRING_FAMILY)
        .setInputExpressionTypes(
            VectorExpressionDescriptor.InputExpressionType.SCALAR,
            VectorExpressionDescriptor.InputExpressionType.COLUMN).build();
  }
Vectorized instruction to concatenate a scalar to a string column and put
the result in an output column.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/StringScalarConcatStringGroupCol.java