As peter's answer you need additional pair(s) of parentheses but still you will get syntax error.
Use a LEFT JOIN operation to create a left outer join
Select dc.*, it.itm_description, pt.pty_name
FROM (dcmst dc LEFT JOIN itemmst it on dc.itm_code = it.itm_code) LEFT JOIN partymst pt on dc.del_pty_code = pt.pty_code