Is right the next query?
<fullquery name="cr_write_content.write_lob_content">
<querytext>
select lob as content
from cr_revisions
where revision_id = :revision_id
</querytext>
</fullquery>
In Oracle this query is :
select content
from cr_revisions
where revision_id = $revision_id
I seen the query in packages/acs-content-repository/tcl/revision-procs-postgres.xql