public Builder appendPositionalParameter() {
            positional = true;
            parameterNames.add(POSITIONAL_PARAM);
            return append(POSITIONAL_PARAM);
        }
Records a positional parameters, and appends a <code>?</code> to the
SQL string.

@return this
core/src/main/java/org/jdbi/v3/core/statement/ParsedSql.java