LakshSingla commented on PR #15700:
URL: https://github.com/apache/druid/pull/15700#issuecomment-1898339465
Thanks for the first PR to Druid! 🚀
A few high level comments with regards to this
1. What's the behaviour if the underlying relation has 0 rows. Shoud it
throw an exception, replace it with null, or replace it with some dummy value
(0.0 for floats, 0 for longs etc). We'd have to see what the SQL standard is or
what other DBs commonly do and model the aggregation on top of it.
2. String and Complex types need to be modeled as well. For string types, it
can be invoked if used with aggregations like `STRLEN`
```sql
SELECT
count(*)
FROM "wiki"
where
col1 >= STRLEN(SELECT dim1 FROM single_row_relation)
```
and with complex types, it can be invoked with functions performing
finalization on the complex types, or something like `PAIR_LEFT` (not yet added
into Druid though). **However** the complex use case seems far-fetched enough,
that we should be fine with saying we don't support such a use case. The
Calcite (or the user) can probably optimize and pushdown the aggregation as
well.
3. Can we implement vector versions of the aggregator as well?
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