解决Oracle ORA-01791 not a SELECTed expression的问题

SELECT distinct pd_crea_co_code FROM pd_project_jx_de LEFT JOIN t_unit ON t_unit.unitno = pd_project_jx_de.pd_crea_co_code LEFT JOIN t_department ON t_department.code = pd_project_jx_de.xmks order by unitname asc;