How to download Postgres bytea column as file

问题

Currently, i have a number of files stored in postgres 8.4 as bytea. The file types are .doc, .odt, .pdf, .txt and etc.

May i know how to download all the file stored in Postgres because i need to to do a backup. I need them in their original file type instead of bytea format.

Thanks!

回答1:

One simple option is to use COPY command with encode to hex format and then apply xxd shell command (with -p continuous hexdump style switch). For example let's say I have jpg image in bytea column in samples table:

\copy (SELECT encode(file, 'hex') FROM samples LIMIT 1) TO
    '/home/grzegorz/Desktop/image.hex'

$ xxd -p -r image.hex > image.jpg

As I checked it works in practice.

回答2:

Try this:

 COPY (SELECT yourbyteacolumn FROM yourtable WHERE <add your clauses here> ...) TO 'youroutputfile' (FORMAT binary)

回答3:

If you have a lot of data to download then you can get the lines first and then iterate through each one writing the bytea field to file.

$resource = pg_connect('host=localhost port=5432 dbname=website user=super password=************');

// grab all the user IDs
$userResponse = pg_query('select distinct(r.id) from resource r
                        join connection c on r.id = c.resource_id_from
                        join resource rfile on c.resource_id_to = rfile.id and         rfile.resource_type_id = 10
                        join file f on rfile.id = f.resource_id
                        join file_type ft on f.file_type_id = ft.id
                        where r.resource_type_id = 38');

// need to work through one by one to handle data
while($user = pg_fetch_array($userResponse)){
    $user_id = $user['id'];
    $query = 'select r.id, f.data, rfile.resource_type_id, ft.extension from resource r
                        join connection c on r.id = c.resource_id_from
                        join resource rfile on c.resource_id_to = rfile.id and rfile.resource_type_id = 10
                        join file f on rfile.id = f.resource_id
                        join file_type ft on f.file_type_id = ft.id
                        where r.resource_type_id = 38 and r.id = ' . $user_id;

    $fileResponse = pg_query($query);
    $fileData = pg_fetch_array($fileResponse);
    $data = pg_unescape_bytea($fileData['data']);
    $extension = $fileData['extension'];
    $fileId = $fileData['id'];
    $filename = $fileId . '.' . $extension;
    $fileHandle = fopen($filename, 'w');
    fwrite($fileHandle, $data);
    fclose($fileHandle);
}

回答4:

Best I'm aware, bytea to file needs to be done at the app level.

(9.1 might change this with the filesystem data wrapper contrib. There's also a lo_export function, but it is not applicable here.)

回答5:

DO $$ 
DECLARE   
   l_lob_id OID;
   r record; BEGIN

  for r in
    select data, filename from bytea_table

   LOOP
    l_lob_id:=lo_from_bytea(0,r.data);
    PERFORM lo_export(l_lob_id,'/home/...'||r.filename);
    PERFORM lo_unlink(l_lob_id);   
    END LOOP;

END; $$

回答6:

Here's the simplest thing I could come up with:

psql -qAt "select encode(file,'base64') from files limit 1" | base64 -d

The -qAt is important as it strips off any formatting of the output. These options are available inside the psql shell, too.

来源：https://stackoverflow.com/questions/6730729/how-to-download-postgres-bytea-column-as-file

标签

file

postgresql

byte