drin commented on issue #38837:
URL: https://github.com/apache/arrow/issues/38837#issuecomment-2129531288

   > The code at this link is not really related to cardinality estimation
   
   Ah, I misunderstood then.
   
   > In DuckDB, these statistics are created as a callback function that exists 
in the scanner
   
   this is why I figured either approach to getting statistics (schema or API 
call) is viable, since the callback should be able to accommodate either.
   
   > Could you explain more about a separate API call
   
   I just meant a function call of the scanner API (or I guess something like 
ADBC, but I don't know that API at all). I interpreted weston's comment to mean 
that a function call to get statistics is comparable to a function call to get 
a record batch.
   
   But when I say it provides extra flexibility, I mean that it provides a 
standard way for an independent producer to specify logic to a consumer for how 
to get statistics. This could allow for things like storing statistics 
independently from the data stream itself. I also feel like this doesn't 
preclude statistics metadata being packed into the schema (maybe in some 
application-specific way).
   


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