For each column that will contain unique references to large objects,

create a <literal>BEFORE UPDATE OR DELETE</> trigger, and give the column

name as the sole trigger argument. You can also restrict the trigger

to only execute on updates to the column with:

<programlisting>

CREATE TRIGGER t_raster BEFORE UPDATE OF raster OR DELETE ON image

FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster);

</programlisting>

to only execute on updates to the column by using <literal>BEFORE UPDATE

OF</literal> <replaceable class="parameter">column_name</replaceable>.

If you need multiple <type>lo</>

columns in the same table, create a separate trigger for each one,

remembering to give a different name to each trigger on the same table.