Обсуждение: Display large object from database

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Display large object from database

От
"Greg"
Дата:

I am using pgSQL 8.1.4. I have a table that stores pictures, using an oid column.

Now using the SQL functions provided I have successfully saved an image to the table, and managed to export it from the table again.

 

I am battling to open the image for reading into a stream.  The mentioned functions support opening for exporting a file in SQL are




SELECT lo_export(image.raster, '/tmp/motd') FROM image
    WHERE name = 'beautiful image';



But how do I open a stream for reading? 




inv_fd = lo_open(conn, inv_oid, INV_READ|INV_WRITE);
 
I have tried to convert this into a SQL statement but INV_READ is not seen as an accepted parameter.

 

Re: Display large object from database

От
Tom Lane
Дата:
"Greg" <greg@officium.co.za> writes:
> I am battling to open the image for reading into a stream.

From what?  The lo_xxx functions are intended to be used from C, not
from SQL.

You might be better off using a bytea column, which is a far simpler
construct than a large object.  It won't give you streamwise access,
just fetch or store the whole value at once, but that might be all you
need.

            regards, tom lane

Re: Display large object from database

От
Дата:
Thanks, I read the pgAdmin help on a bytea column, but it doesn't specify its maximum size. What is
the largest filesize I can fit into a bytea column?

Thanks

----- Original Message -----
From: Tom Lane
To:
Cc: pgsql-novice@postgresql.org
Sent:  Mon, 05 Jun 2006 10:55:26 -0400
Subject: Re: [NOVICE] Display large object from database

"Greg" <greg@officium.co.za> writes:
> I am battling to open the image for reading into a stream.

From what?  The lo_xxx functions are intended to be used from C, not
from SQL.

You might be better off using a bytea column, which is a far simpler
construct than a large object.  It won't give you streamwise access,
just fetch or store the whole value at once, but that might be all you
need.

            regards, tom lane

Re: Display large object from database

От
Tom Lane
Дата:
<greg@officium.co.za> writes:
> Thanks, I read the pgAdmin help on a bytea column, but it doesn't specify its maximum size. What is
> the largest filesize I can fit into a bytea column?

The hard limit is 1Gb.  Practical limit is probably a good deal less,
depending on your machine, but I don't know of anyone who's tried to
measure performance with such wide column values.

            regards, tom lane