public String getAdditionalKey() {
        return additionalKey;
    }
Returns the additional key if data type is {@link RedisDataType#HASH} and {@link RedisDataType#SORTED_SET}.

@return the additional key
inlong-sort/sort-flink/sort-flink-v1.15/sort-connectors/redis/src/main/java/org/apache/inlong/sort/redis/common/mapper/RedisCommandDescription.java