mysql - 左加入学生付款

Question

我这里有个问题。我有4张表，分别是:students, fee, payments and class

学生

(student_id, firstname, lastname, cellphone, email, address, photofile, class_id)

类

(class_id, class_description, class_date, class_venue)

付款

(payment_id, student_id, payment_date, payment_amount, fee_id)

费用

(fee_id, fee_description, class_id, fee_amount)

基本上，我需要创建一个查询，该查询能够显示学生是否根据 进行了付款 费用。但是，我已经尝试了从 stackoverflow 获得的所有左连接，但仍然无法获得我想要的结果。

我有这个:

SELECT 
students.student_id, fee.fee_id, fee.fee_description,
fee.class_id, fee.fee_amount, students.firstname, students.lastname,
payments.payment_id, payments.payment_date 

FROM students 
LEFT JOIN class ON students.class_id = class.class_id 
LEFT JOIN fee ON fee.class_id = class.class_id 
LEFT JOIN payments ON payments.student_id = students.student_id

然后我得到如下结果:

+-----------+--------+---------------------+-----------+-------------+-----------+----------+------------+--------------+
|student_id | fee_id | fee_description     | class_id  | fee_amount  | firstname | lastname | payment_id | payment_date |
+-----------+--------+---------------------+-----------+-------------+-----------+----------+------------+--------------+
|     1     |   1    | Secondary Malay@Dec |     1     |     50      |  Bob      |   Smith  |     1      | 2013-12-18   |
|     1     |   1    | Secondary Malay@Dec |     1     |     50      |  Bob      |   Smith  |     11     | 2013-12-27   |
|     1     |   5    | Secondary Malay@Jan |     1     |     50      |  Bob      |   Smith  |     1      | 2013-12-18   |
|     1     |   5    | Secondary Malay@Jan |     1     |     50      |  Bob      |   Smith  |     11     | 2013-12-27   |
|     2     |   2    | Primary Eng@Dec     |     2     |     35      |  Joe      |   Doe    |     10     | 2013-12-02   |
|     11    |   1    | Secondary Malay@Dec |     1     |     50      |  Bryant   |   Quan   |     8      | 2013-12-19   |
|     11    |   5    | Secondary Malay@Jan |     1     |     50      |  Bryant   |   Quan   |     8      | 2013-12-19   |
+-----------+--------+---------------------+-----------+-------------+-----------+----------+------------+--------------+

问题:

• 学生 (Bob Smith) 出现了 4 次(应该只出现两次 - 12 月和 1 月费用)。
• 学生 (Bryant Quan) 只支付了 12 月的费用，但查询显示他也支付了 1 月的费用。
• payment_id 应该是唯一的，因此不能出现超过 1 次。

目前，我正在使用 Flash Builder 开发移动应用程序。该应用程序用于跟踪学生的付款，因此，我需要先解决此问题，然后再进行其他操作。如果有人知道如何，请指导我完成此操作。提前谢谢你><"

mysql源代码在这里:http://sqlfiddle.com/#!2/d4482a

Answer 1

在 feeid 上加入付款和费用表，应该会给您正确的结果

编辑:

SELECT 
students.student_id, fee.fee_id, fee.fee_description,
fee.class_id, fee.fee_amount, students.firstname, students.lastname,
payments.payment_id, payments.payment_date 

FROM students 
LEFT JOIN class ON students.class_id = class.class_id 
LEFT JOIN fee ON fee.class_id = class.class_id 
LEFT JOIN payments ON payments.student_id = students.student_id and Payments.fee_id = fee.fee_id

这会给你所有已经支付和未支付的学生 您可以根据需要使用 where payment_id is null 或 is not null 对其进行过滤 如果 payment_id 为 null，则表示他们尚未付款，否则已付款