Re: COPY enhancements

Emmanuel Cecchet <manu(at)frogthinker(dot)org> writes:
> Tom was also suggesting 'refactoring COPY into a series of steps that the
> user can control'. What would these steps be? Would that be per row and
> allow to discard a bad tuple?

The idea is to have COPY usable from a general SELECT query so that the
user control what happens. Think of an SRF returning bytea[] or some
variation on the theme.

Maybe WITH to the rescue:

WITH csv AS (
-- no error here as the destination table is in memory tuple store,
-- assuming we have adunstan patch to ignore rows with too few or
-- too many columns
COPY csv(a, b, c, d) FROM STDIN WITH CSV HEADER --- and said options
)
INSERT INTO destination
SELECT a, b, f(a + b - d), strange_timestamp_reader(c)
FROM csv
WHERE validity_check_passes(a, b, c, d);

That offers complete control to the user about the stages that transform
the data. In a previous thread some ideas I forgot the details offered
to the users some more control, but I don't have the time right now to
search in the archives.

Regards,
--
Dimitri Fontaine
PostgreSQL DBA, Architecte