Question

我目前是SQL语言的新手，我很难理解如何从下表中检索正确的信息：

员工表

+------+----------+---------+-----------------+------+------+
| s_id | initials | s_name  | pos             | qual | d_id |
+------+----------+---------+-----------------+------+------+
| AA   | A.       | Tom     | Lecturer        | PhD  | RELI |
| BBB  | J.J.     | Jason   | Senior Lecturer | PhD  | RELI |
| CCC  | B.A.     | Andy    | Senior Lecturer | PhD  | BIOL |
| DD   | M.       | Mark    | Professor       | PhD  | BIOL |
| EE   | W.       | Alen    | Professor       | BA   | BIOL |
+------+----------+---------+-----------------+------+------+

研究表

+------+-------+------------+-----------+
| s_id | r_id  | str_date   | fin_date  |
+------+-------+------------+-----------+
| BBB  | RESH1 |       1990 |      1998 |
| BBB  | RESH2 |       1980 |      1985 |
| DD   | RESH4 |       1995 |      1999 |
| AA   | RESH4 |       1992 |      1999 |
| CCC  | RESH8 |       1989 |      1994 |
| EE   | RESH5 |       1988 |      1989 |
+------+-------+------------+-----------+

我正在尝试创建一个新表，其中包含staff s_name以及每个人进行了多少次不同的研究。

到目前为止我所拥有的是

select distinct s.s_name, count(r.s_id) 
from staff s 
inner join research r 
on s.s_id = r.s_id 
where s.s_id = r.s_id;

我的结果是，

+---------+---------------+
| s_name  | count(r.s_id) |
+---------+---------------+
| Jason   |             6 |
+---------+---------------+

我做错了什么？

提前致谢。

Answer 1

我认为这样做：

select s.s_name, count(*) 
from staff s 
inner join research r 
on s.s_id = r.s_id 
group by r.s_id

Answer 2

比较Staff表和research表之间的S_ID数据类型。任何一个表中都可能有空格。否则，请在连接条件中使用Trim函数，以便可以收到正确的结果集。

您的查询仅返回Staff表中的不同ID。您应该在SQL语句中使用group by。

希望这有帮助！

从两个不同的表中检索信息

2 个答案: