Re: csv_populate_recordset and csv_agg

Steve Chavez <steve(at)supabase(dot)io> writes:
> CSV processing is also a common use case and PostgreSQL has the COPY ..
> FROM .. CSV form but COPY is not compatible with libpq pipeline mode and
> the interface is clunkier to use.

> I propose to include two new functions:

> - csv_populate_recordset ( base anyelement, from_csv text )
> - csv_agg ( anyelement )

The trouble with CSV is there are so many mildly-incompatible
versions of it. I'm okay with supporting it in COPY, where
we have the freedom to add random sub-options (QUOTE, ESCAPE,
FORCE_QUOTE, yadda yadda) to cope with those variants.
I don't see a nice way to handle that issue in the functions
you propose --- you'd have to assume that there is One True CSV,
which sadly ain't so, or else complicate the functions beyond
usability.

Also, in the end CSV is a surface presentation layer, and as
such it's not terribly well suited as the calculation representation
for aggregates and other functions. I think these proposed functions
would have pretty terrible performance as a consequence of the
need to constantly re-parse the surface format. The same point
could be made about JSON ... which is why we prefer to implement
processing functions with JSONB.

regards, tom lane