private ValueExtractor buildTagFieldValueExtractor(final String fieldName, final int fieldIndex) {
        return (rs, arr, cache) -> {
            Val value = cache.get(fieldName);
            if (value == null) {
                //populate our cache of
                cache.putAll(extractTagsMapFromColumn(getResultSetString(rs, SQLStatisticNames.NAME)));
            }
            value = cache.get(fieldName);
            arr[fieldIndex] = value;
        };
    }
Build a mapper function that will only extract the columns of interest from the resultSet row.
Assumes something external to the returned function will advance the resultSet
stroom-statistics/stroom-statistics-impl-sql/src/main/java/stroom/statistics/impl/sql/search/StatisticsSearchServiceImpl.java