select deptno ,avg(sal)
from emp
group by deptno ; --按照部門編號分組
select a,b,c ，組函數(x)
from table
group by a ; --這里應該寫a,b,c 不能只寫a 通過部門號 然后通過b c條件接著分組
只寫a ora-00937 非法使用分組函數
在select 列表中所有未包含的組函數中的列 group by中都應該寫
select avg(sal)
from emp
group by deptno; --這種不會展示deptno
select
pm_ci.ci_id as ci_id
, listagg(to_char(pm_stu.stu_name), ',') within group(order by pm_stu.stu_id) as stu_name
from
pm_ci
inner join pm_stu
on substr(pm_ci.stu_id, instr(pm_ci.stu_id, pm_stu.stu_id),1) = pm_stu.stu_id
group by pm_ci.ci_id;
select
pm_ci.ci_id as ci_id
, listagg(to_char(pm_stu.stu_name), ',') within group(order by pm_stu.stu_id) as stu_name
from
pm_ci
inner join pm_stu
on instr(pm_ci.stu_id, pm_stu.stu_id) > 0
group by pm_ci.ci_id;
