PostgreSQL 9.3.25 Documentation | ||||
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There are server-side functions callable from SQL that
correspond to each of the client-side functions described above;
indeed, for the most part the client-side functions are simply
interfaces to the equivalent server-side functions. The ones that
are actually useful to call via SQL commands are lo_creat
, lo_create
, lo_unlink
, lo_import
, and lo_export
. Here are examples of their use:
CREATE TABLE image ( name text, raster oid ); SELECT lo_creat(-1); -- returns OID of new, empty large object SELECT lo_create(43213); -- attempts to create large object with OID 43213 SELECT lo_unlink(173454); -- deletes large object with OID 173454 INSERT INTO image (name, raster) VALUES ('beautiful image', lo_import('/etc/motd')); INSERT INTO image (name, raster) -- same as above, but specify OID to use VALUES ('beautiful image', lo_import('/etc/motd', 68583)); SELECT lo_export(image.raster, '/tmp/motd') FROM image WHERE name = 'beautiful image';
The server-side lo_import
and
lo_export
functions behave
considerably differently from their client-side analogs. These two
functions read and write files in the server's file system, using
the permissions of the database's owning user. Therefore, their use
is restricted to superusers. In contrast, the client-side import
and export functions read and write files in the client's file
system, using the permissions of the client program. The
client-side functions do not require superuser privilege.
The functionality of lo_read
and
lo_write
is also available via
server-side calls, but the names of the server-side functions
differ from the client side interfaces in that they do not contain
underscores. You must call these functions as loread
and lowrite
.