Apache Druid

try
```select count(distinct item, year, location) from tableA```

You can try this
```SELECT COUNT(DISTINCT ARRAY[item, year, location]) from tableA```

it seems that we currently don't support using multiple fields in a approximate count aggregation via SQL.

oh okay so then Native query is the only option

CardinalityAggregatorFactory accepts multiple fields already. It seemed trivial to support that in SQL.

yeah. It would need changes in `BuiltinApproxCountDistinctSqlAggregator`

<https://github.com/apache/druid/pull/13014/files>

in the meantime, you can also use concat like `APPROX_COUNT_DISTINCT_DS_HLL(item || year || location)` or get fancy with separators `APPROX_COUNT_DISTINCT_DS_HLL(item || ':' || year || ':' || location)`

It's not as fast as the native option (it has to actually compute the concatted string) but it would work

Thanks <@U0344FW86DD>. the reason i am doing this is to get approx count of the records i will be reading in my application before actually firing the actual query so that i can limit the data if needed.
i am sticking to the Native query as response time is a important factor. Do you think this is the right way to go for getting the approx count of the query before actually firing the query ?