Mysql 如何通过计数将一个组从一个关系关联到另一个关系？

我有以下两种模式：

advisor(s_ID, i_ID)
instructor(ID, name, dept_name, credits)

我已通过以下方式计算每个不同I_ID的I_ID出现总数：

SELECT i_ID, count(*)
FROM advisor
GROUP BY i_ID;

每个ID都属于一个部门名称。如何获取每个部门名称出现的总数

例如：

i_ID     count 
21         3
23         4
27         1
29         5

假设i_ID 21,23属于讲师（ID，物理），i_ID 27,29属于讲师（ID，化学），则输出为：

dept_name   count
physics       7(3+4)
chemistry     6(1+5)

试试这个

  select a.dept_name,count(*) as count from instructor a join advisor b
    on a.ID=b.i_ID group by  a.ID

试试这个

  select a.dept_name,count(*) as count from instructor a join advisor b
    on a.ID=b.i_ID group by  a.ID

我希望这有帮助

select dept name, 0 as total advised
from (select dept name from department
minus
select dept name
from instructor)
union
select dept name, count(*) as total advised
from instructor, advisor
where instructor.id = advisor.I ID
group by dept name
order by dept name;

我希望这有帮助

select dept name, 0 as total advised
from (select dept name from department
minus
select dept name
from instructor)
union
select dept name, count(*) as total advised
from instructor, advisor
where instructor.id = advisor.I ID
group by dept name
order by dept name;

---

i_ID是外键。我说得对吗？是的，你说得对。虽然它在讲师中被命名为ID。i_ID是外键。我说得对吗？是的，你说得对。尽管它在讲师中被命名为ID。