Re: Re: csv format for psql

2018-03-24 8:15 GMT+01:00 Fabien COELHO <coelho@cri.ensmp.fr>:

>
> Hello Pavel,
>
> The patch adds a simple way to generate csv output from "psql" queries,
>>> much simpler than playing around with COPY or \copy. It allows to
>>> generate
>>> a clean CSV dump from something as short as:
>>>
>>>   sh> psql --csv -c 'TABLE foo' > foo.csv
>>>
>>> Documentation is clear.
>>>
>>> Test cover a significant number of cases (fieldsep, expanded,
>>> tuples-only).
>>> Although recordsep changes are not actually tested, it worked
>>> interactively
>>> and I think that tests are sufficient as is.
>>>
>>> There are somehow remaining point about which a committer/other people
>>> input would be nice:
>>>
>>> (1) There are some mild disagreement whether the fieldsep should be
>>> format specific shared with other format. I do not think that a specific
>>> fieldsep is worth it, but this is a marginal preference, and other people
>>> opinion differ. What is best is not obvious.
>>>
>>> Pavel also suggested to have a special handling based on whether the
>>> fieldsep is explicitely set or not. I'm not too keen on that because it
>>> departs significantly from the way psql formatting is currently handled,
>>> and what is happening becomes unclear to the user.
>>>
>>> (2) For interactive use, two commands are required: \pset format csv +
>>> \pset fieldsep ',' (or ';' or '\t' or whatever...). Maybe some \csv command
>>> similar to \H would be appropriate, or not, to set both values more
>>> efficiently. Could be something for another patch.
>>>
>>> Not sure what is the status of the patch if we do not have a clear
>>> consensus.
>>>
>>
>> I am sorry, but I don't think so this interface is good enough. Using | as
>> default CSV separator is just wrong. It and only it is a problem. Any
>> other
>> is perfect.
>>
>
> I do not think that there is a perfect solution, so some compromise will
> be needed or we won't get it.
>
> (1) patch v4:
>
>     "\pset format csv" retains the current fieldsep value, so fields are
>     separated by whatever is in the variable, which means that for getting
>     a standard csv two commands are needed, which is clearly documented,
>     but may be considered as surprising. ISTM that the underlying point is
>     that "format" is really about string escaping, not about the full
> output
>     format, but this is a pre-existing situation.
>
>     I'm suggesting to add \csv which would behave like \H to toggle CSV
>     mode so as to improve this situation, with a caveat which is that
>     toggling back \csv would have forgotted the previous settings (just
>     like \H does, though, so would for instance reset to aligned with |),
>     so it would not be perfect.
>

this doesn't solve usual format settings by \pset format csv


>
> (2) your proposal as I understand it:
>
>     "\pset format csv" may or may not use the fieldsep, depending on
>     whether it was explicitely set, an information which is not shown,
> i.e.:
>
>       \pset fieldsep # fieldsep separator is "|"
>       \pset format csv # would output a,b,c or a|b|c...
>
>     Because it depends on whether fieldsep was set explicitely to '|' or
>     whether it has this value but it was due to the default.
>
>     This kind of unclear behavioral determinism does not seem desirable.
>

please, check and test attached patch. It is very simply for usage - and
there is not any unclear behave. Just you should to accept so formats can
have own defaults for separators.


>
> (3) other option, always use a comma:
>
>     this was rejected because some people like their comma separated
>     values to be separated by semi-colons or tabs (aka tsv).
>
> (4) other option, Daniel v3 or v2:
>
>     use a distinct "fieldsep_csv" variable initially set to ','. This adds
>     yet another specific variable that has to be remembered, some styles
>     would use fieldsep but csv would not so it is some kind of exception
>     that I would wish to avoid.
>
> My current preference order in the suggested solutions is 1, 4, 2, 3, with
> a significant preference for 1.
>

I am thinking so @1 solves nothing - people are using \pset format ...

@3 is clearly bad - there are not any discussion

@4 can be compromise solution, but then there should be renamed fieldsep.
Now, fieldsep is used just for unaligned format - for nothing else. If we
introduce fieldsep_csv, then fieldsep should be renamed to
fieldsep_unaligned. I can live with it.

But I think so default fieldsep is better option. Please, try my patch and
comment it.

Regards

Pavel

>
> --
> Fabien.
>