Question

这些是我的表

mysql> select * from professor;
    +-------+--------+--------+--------+------+
    | empid | name   | status | salary | age  |
    +-------+--------+--------+--------+------+
    |     1 | Arun   |      1 |   2000 |   23 |
    |     2 | Benoy  |      0 |   3000 |   25 |
    |     3 | Chacko |      1 |   1000 |   36 |
    |     4 | Divin  |      0 |   5000 |   32 |
    |     5 | Edwin  |      1 |   2500 |   55 |
    +-------+--------+--------+--------+------+
    5 rows in set (0.00 sec)

mysql> select * from works;
+----------+-------+---------+
| courseid | empid | classid |
+----------+-------+---------+
|        1 |     1 |      10 |
|        2 |     2 |       9 |
|        3 |     3 |       8 |
|        4 |     4 |      10 |
|        5 |     5 |       9 |
|        6 |     1 |       9 |
|        2 |     3 |      10 |
|        2 |     1 |       7 |
|        4 |     2 |       6 |
|        7 |     5 |       6 |
|        3 |     5 |       2 |
|        2 |     4 |       6 |
|        2 |     5 |       2 |
+----------+-------+---------+
15 rows in set (0.00 sec)

mysql> select * from course;
+----------+------------+--------+
| courseid | coursename | points |
+----------+------------+--------+
|        1 | Maths      |      4 |
|        2 | Science    |      4 |
|        3 | English    |     85 |
|        4 | Social     |      4 |
|        5 | Malayalam  |     99 |
|        6 | Arts       |     40 |
|        7 | Biology    |    100 |
+----------+------------+--------+
7 rows in set (0.00 sec)

问题是：

Return the names of full professors who have taught at least two courses in one Class

我的查询是：

select professor.name from professor
inner join works
on professor.empid=works.empid
group by works.empid
having count(distinct works.courseid)>=2

我现在得到的输出是：

Arun
Benoy
Chacko
Divin
Edwin

我应该把输出称为'Edwin'，因为他是唯一一个在同一课堂上教过两门科目的人。请帮忙

Answer 1

你必须考虑你的小组是错误的改变它

   group by classid,works.empid

就像那样，你将在classid中计算courseid。

mysql使用group by连接

1 个答案: