代码：

Question

所以我有4张表通过外键连接，即结果，位置，学生，候选人

我需要实现的是：输出：

------------------------
 s_fname | count(c_id)
-----------------------
   Mark  |     2       -> President
   France|     2       -> President

..计算c_id在表格中重复了多少次＆＃34;结果＆＃34;这也是由＆＃34;候选人＆＃34;中的pos_id过滤的。表

以下是我的代码，缺少计数部分：

select s_fname 
from results, candidates, student, positioning 
where results.c_id = candidates.c_id 
  AND student.sid = results.sid 
  AND candidates.pos_id = positioning.pos_id 
  AND positioning.pos_id = 1 
Group BY results.sid;

..我知道它缺少很多东西......

由于

对我而言似乎非常复杂，但我知道这里有大师可以实现这一目标，

结果表

---------------------
| r_id | sid | c_id |
---------------------
    1   |  1  |   1
    2   |  1  |   2
    3   |  1  |   4
    4   |  2  |   1
    5   |  2  |   2
    6   |  2  |   4
    7   |  3  |   3
    8   |  3  |   2
    9   |  5  |   3
    10  |  5  |   2

----------------------
student table
----------------
| s_id| s_fname|
----------------
    1  |  Mark
    2  |  Jorge
    3  |  France
    4  |  James

--------------------
Candidates Table
------------------------
| c_id | sid  |  pos_id
------------------------
    1   |   1  |     1
    2   |   2  |     2
    3   |   4  |     3
    4   |   3  |     1
    5   |   5  |     2


----------------------
positioning Table
-----------------------
| pos_id  |  po_name |
-----------------------
 1    |  President
 2    |  Vice President
 3    |  Secretary
 4    |  Treasurer

Answer 1

这是未经测试的，但应该返回您的预期结果。

它的作用是加入相关foreign keys上的所有表格，有效地提供了所有列的宽表格。然后，我们限制为candidates位置运行的President。由于group上的count aggregate我们group，我们需要name。 count应该反映他们获得的投票数，因为one to many relationship表格有result。

SELECT s_fname, Count(*) 
FROM studentTable st 
INNER JOIN Candidates c On c.sid = st.s_ID 
INNER JOIN positioning p on c.pos_ID = p.pos_ID
INNER JOIN results r on st.s_ID = r.s_ID
WHERE po_Name = "President"
GROUP BY s_Fname

由于对预期连接的误解，以下查询应显示适当的结果。

SELECT s_fname, Count(*) 
FROM studentTable st 
INNER JOIN Candidates c On c.sid = st.s_ID 
INNER JOIN positioning p on c.pos_ID = p.pos_ID
INNER JOIN results r on c.c_ID = r.c_ID
WHERE po_Name = "President"
GROUP BY s_Fname

Answer 2

代码：

SELECT s_fname AS [Student Name], COUNT(A.c_id) AS [Count], po_name AS [Position]
FROM results AS A INNER JOIN candidates AS B ON A.c_id=B.c_id
                  INNER JOIN student AS C ON A.sid=C.sid
                  INNER JOIN positioning AS D ON B.pos_id=D.pos_id
WHERE B.pos_id = 1 
GROUP BY s_fname

Answer 3

SELECT s.s_fname, COUNT(*), p.po_name
    FROM students s 
    JOIN candidates c ON c.s_id = s.s_id
    JOIN positioning p ON c.pos_id = p.pos_id
    JOIN results r ON s.s_id = r.s_id
WHERE p.pos_id = 1
GROUP BY s.s_id

http://sqlfiddle.com/#!2/9472a/17

如何编写这个基本的sql语句

3 个答案:

代码：