MySQL的INNER JOIN

Question

我使用以下查询来获取不同的表我的数据库，检查报告如下......

SELECT s.id, s.name, c.name AS course_name, 
s.open_bal AS open_balance, sum(i.amount) AS gross_fee, 
sum(i.discount) AS discount, sum(i.amount) - sum(i.discount) AS net_payable, 
SUM(r.reg_fee+r.tut_fee+r.other_fee) AS net_recieved, 
(sum(i.amount) - sum(i.discount)) - SUM(r.reg_fee+r.tut_fee+r.other_fee) AS balance_due 
FROM students s 
INNER JOIN courses c on c.id = s.course_id 
LEFT JOIN invoices i on i.student_id = s.id 
LEFT JOIN recipts r on r.student_id = s.id; 

发票

| id | student_id | amount | discount | dnt  | 
+----+------------+----------+----------+-------------+ 
| 2 | 22   | 35000 | 0  | 2011/01/01 | 
+----+------------+----------+----------+-------------+ 

没有得到来自gross_fee和net_payable正确的值。

谢谢。

Answer 1

鉴于SUM s在选择我想GROUP BY s.id应该做的伎俩。反正一个GROUP BY似乎缺少:)

SELECT s.id, s.name, c.name AS course_name, 
s.open_bal AS open_balance, 
SUM(r.reg_fee+r.tut_fee+r.other_fee) AS net_recieved, 
(sum(i.amount) - sum(i.discount)) - SUM(r.reg_fee+r.tut_fee+r.other_fee) AS balance_due 
FROM students s 
INNER JOIN courses c on c.id = s.course_id 
LEFT JOIN invoices i on i.student_id = s.id 
LEFT JOIN recipts r on r.student_id = s.id 
GROUP BY s.id; 

编辑

单独的查询允许检索gross_fee和net_payable所有发票

SELECT sum(amount) AS gross_fee, 
    sum(discount) AS discount, 
    sum(amount) - sum(discount) AS net_payable, 
FROM invoices; 

Answer 2

同时拥有学生记录得到的值为s.course_id？

你有一个内从学生的课程加入...

INNER JOIN横列C上c.id = s.course_id

如果s.course_id中的学生记录为null ，查询将只返回一行。