Re: export import bytea from psql

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});

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
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