例如：查询所有学生的选课情况

Oracle写法：

SELECT s.SNAME,st.COURSE
  FROM tt_student s,(SELECT sc.SNO,wmsys.wm_concat(tc.CNAME) COURSE
          FROM SC sc
         INNER JOIN tt_course tc
            ON tc.CNO = sc.CNO
         GROUP BY sc.SNO) st
 WHERE s.SNO = st.SNO

SELECT s.SNAME,group_concat(tc.CNAME) COURSE
          FROM SC sc
         INNER JOIN tt_course tc
            ON tc.CNO = sc.CNO
         GROUP BY sc.SNO) st
 WHERE s.SNO = st.SNO