Re: copying json data and backslashes - Mailing list pgsql-general

> From: pbj@cmicdo.com <pbj@cmicdo.com>
> Sent: 22 November 2022 15:30
> To: Alastair McKinley <a.mckinley@analyticsengines.com>; pgsql-general@lists.postgresql.org
<pgsql-general@lists.postgresql.org>;Erik Wienhold <ewie@ewie.name> 
> Subject: Re: copying json data and backslashes
>  
>  >
>  > On Tuesday, November 22, 2022 at 10:16:11 AM EST, Erik Wienhold <ewie@ewie.name> wrote:
>  >
>  >
>  > > On 22/11/2022 15:23 CET Alastair McKinley <a.mckinley@analyticsengines.com> wrote:
>  > >
>  > > Hi all,
>  > >
>  > > I have come across this apparently common issue COPY-ing json and wondering if
>  > > there is potentially a better solution.
>  > >
>  > > I am copying data into a jsonb column originating from a 3rd party API. The
>  > > data may have literal \r,\t,\n and also double backslashes.
>  > >
>  > > I discovered that I can cast this data to a jsonb value directly but I can't
>  > > COPY the data without pre-processing.
>  >
>  >
>  > > Is there any other solution with COPY that doesn't require manual
>  > > implementation of search/replace to handle these edge cases?
>  > > Why does ::jsonb work but COPY doesn't? It seems a bit inconsistent.
>  >
>  > COPY handles special backslash sequences[1].  The \r in your sample JSON,
>  > although properly escaped according to JSON, is replaced with an actual
>  > carriage return by COPY before casting to jsonb.  The error results from JSON
>  > prohibiting unescaped control characters in strings[2].
>  >
>  > You must double escape to pass those characters through COPY.
>  >
>  > See how COPY outputs backslash sequences:
>  >
>  >     -- Actual carriage return:
>  >     copy (select e'\r') to stdout;
>  >     \r
>  >
>  >     -- Backslash sequence for carriage return:
>  >     copy (select '\r') to stdout;
>  >
>  >     \\r
>
> I have been able to get around this problem by using the following method:
>
> \copy footable from 'input.json' (format csv, escape '^B', delimieter '^C', quote '^E')
>
> where the control characters are the actual control char, not the caret-letter, and it requires no escaping escapes. 
Irealize this won't work for all 
> situations.
>
> PJ

Hi PJ,

Thanks for the suggestion, this is interesting to me to try but I am not quite sure how this works.
As far as I understand, escape/quote/delimiter have to be a single character, and CTRL-C etc. are multiple characters.

What way do you input each of the escape/quote/delimiter characters?

Best regards,

Alastair

>
>  >
>  > [1]
>  > https://www.postgresql.org/docs/current/sql-copy.html#id-1.9.3.55.9.2
>  > [2] https://www.json.org/json-en.html
>  >
>  > --
>  > Erik
>