MySQL 语句连接 2 个表并对相同项目数量求和

Question

我有 2 个表，客户和交易。

Customer:
--------------------------------------------
ID | Name            | Tel
--------------------------------------------
1  | Peter           | 123 4567
2  | John            | 456 1234
3  | Alice           | 789 4561
4  | Amy             | 741 8525

Transaction:
--------------------------------------------
CustID | Books | Pens  | Ruler
--------------------------------------------
  1    |   2   |  0    |   1
  2    |   1   |  0    |   0
  1    |   0   |  3    |   0
  1    |   0   |  0    |   1
  2    |   1   |  1    |   1
  3    |   0   |  2    |   2

我需要以下内容

Results:
-------------------------------------------------------------------
ID | Name          | Tel            | Books | Pens  | Ruler
-------------------------------------------------------------------
1  | Peter         | 123 4567       |   2   |   3   |   2
2  | John          | 456 1234       |   2   |   1   |   1
3  | Alice         | 789 4561       |   0   |   2   |   2
4  | Amy           | 741 8525       |   0   |   0   |   0

基本上它会将同一客户的书籍、钢笔和尺子相加。

我试过了：

                        $sql = "select 
                                    `customer`.id,
                                    `custmaster`.name,
                                    `custmaster`.tel,
                                    `transaction`.id,
                                    `transaction`.books,
                                    `transaction`.pens,
                                    `transaction`.ruler,
                                from `customer` 
                                left join `transaction` 
                                on `customer`.id=`transaction`.custid 
                                ORDER BY `customer`.id ASC";

但不显示。 :( 我确实知道我在某个地方需要 sum() 函数。有人可以帮忙吗？

Answer 1

使用SUM 和GROUP BY。

SELECT c.id, c.name, c.tel, SUM(t.books) as books, SUM(t.pens) AS pens, SUM(t.ruler) AS ruler
FROM customer AS c
LEFT JOIN transactions AS t ON c.id = t.custid
GROUP BY c.id
ORDER BY c.id

Answer 2

试试这个方法

select 
    `customer`.id,
    `custmaster`.name,
    `custmaster`.tel,
    `transaction`.id,
    sum(`transaction`.books) as books,
    sum(`transaction`.pens) as pens,
    sum(`transaction`.ruler) as ruler,
from `customer` 
left join `transaction` 
on `customer`.id=`transaction`.custid
Group by `customer`.id,`customer`.Name
ORDER BY `customer`.id ASC";