CREATE or replace FUNCTION one(text)
RETURNS text AS '
declare

        uname_in alias for $1;
        return_holder xxx.filename%type;
begin
        SELECT into return_holder filename from xxx where description  like ''%'' || uname_in ||''%''; 
        IF FOUND THEN 
                return return_holder;
        ELSE    
                return ''not found'';
        END IF;

end;
'
LANGUAGE 'plpgsql';