Re: POC PATCH: copy from ... exceptions to: (was Re: VLDB Features)

On Thu, Nov 9, 2023 at 4:12 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Daniel Gustafsson <daniel(at)yesql(dot)se> writes:
> >> On 8 Nov 2023, at 19:18, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> I think an actually usable feature of this sort would involve
> >> copying all the failed lines to some alternate output medium,
> >> perhaps a second table with a TEXT column to receive the original
> >> data line. (Or maybe an array of text that could receive the
> >> broken-down field values?) Maybe we could dump the message info,
> >> line number, field name etc into additional columns.
>
> > I agree that the errors should be easily visible to the user in some way. The
> > feature is for sure interesting, especially in data warehouse type jobs where
> > dirty data is often ingested.
>
> I agree it's interesting, but we need to get it right the first time.
>
> Here is a very straw-man-level sketch of what I think might work.
> The option to COPY FROM looks something like
>
> ERRORS TO other_table_name (item [, item [, ...]])
>
> where the "items" are keywords identifying the information item
> we will insert into each successive column of the target table.
> This design allows the user to decide which items are of use
> to them. I envision items like
>
> LINENO bigint COPY line number, counting from 1
> LINE text raw text of line (after encoding conversion)
> FIELDS text[] separated, de-escaped string fields (the data
> that was or would be fed to input functions)
> FIELD text name of troublesome field, if field-specific
> MESSAGE text error message text
> DETAIL text error message detail, if any
> SQLSTATE text error SQLSTATE code
>

just
SAVE ERRORS

automatically create a table to hold the error. (validate
auto-generated table name uniqueness, validate create privilege).
and the table will have the above related info. if no error then table
gets dropped.