SELECT a.ci_id, wm_concat(b.stu_name) FROM (SELECT ci_id, substr(stu_ids, instr(stu_ids, stu_id), length(stu_id)) AS stu_id FROM pm_ci, pm_stu WHERE stu_id =
substr(stu_ids, instr(stu_ids, stu_id), length(stu_id))) a,
pm_stu b
WHERE a.stu_id = b.stu_id
GROUP BY a.ci_id;
右外连接 ：(取右表的全部）
select d.deptno 部门号,d.dname 部门名称,count(e.empno) 人数
from emp e,dept d
where e.deptno(+)=d.deptno
group by d.deptno,d.dname;
左外连接：(取左表的全部）
select d.deptno 部门号,d.dname 部门名称,count(e.empno) 人数
from dept d,emp e
where d.deptno=e.deptno(+)
group by d.deptno,d.dname;
我分析应先这样
select *
from pm_ci a,pm_stu b
然后
select a.ci_id,instr(a.stu_ids,b.stu_id)
from pm_ci a, pm_stu b;
前面有个例子
select deptno,wm_concat(ename) from emp group by deptno;
之后又这样一下
select deptno,ename from emp;
然后就卡住了
