Re: [HACKERS] export import bytea from psql - Mailing list pgsql-hackers

From Pavel Stehule
Subject Re: [HACKERS] export import bytea from psql
Date
Msg-id CAFj8pRDXtoYhauX8gkWexUq0FYtXc9LhkM1nsMVND6uCYNZXfw@mail.gmail.com
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In response to Re: [HACKERS] export import bytea from psql  ("Daniel Verite" <daniel@manitou-mail.org>)
Responses Re: [HACKERS] export import bytea from psql  ("Daniel Verite" <daniel@manitou-mail.org>)
List pgsql-hackers


2017-05-09 23:00 GMT+02:00 Daniel Verite <daniel@manitou-mail.org>:
        Pavel Stehule wrote:

> 1. using psql variables - we just need to write commands \setfrom
> \setfrombf - this should be very simple implementation. The value can be
> used more times. On second hand - the loaded variable can hold lot of
> memory (and it can be invisible for user).

This could be simplified by using the variable only for the filename,
and then injecting the contents of the file into the PQexec'd query
as the interpolation of the variable.
We already have:
 :var for verbatim injection
 :'var' for injection quoted-as-text
 :"var" for injection quoted-as-identifier

What if we add new forms of dereferencing, for instance
(not necessarily with this exact syntax):
 :<var> for injecting the quoted-as-text contents of the file pointed
  to by var.
 :{var} same thing but with file contents quoted as binary
 (PQescapeByteaConn)

then we could write:

\set img '/path/to/image.png'
insert into image(binary) values(:{img});

It is similar to my first or second proposal - rejected by Tom :(
 

We could also go further  in that direction. More new interpolation
syntax could express that a variable is to be passed as a
parameter rather than injected (assuming a parametrized query),
and whether the value is directly the contents or it's a filename
pointing to the contents, and whether its format is binary or text,
and even support an optional oid or typename coupled to
the variable.
That would be a lot of new syntax for interpolation but no new
backslash command and no change to \set itself.


Best regards,
--
Daniel Vérité
PostgreSQL-powered mailer: http://www.manitou-mail.org
Twitter: @DanielVerite

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