codeigniter中SQL列的总和

Question

我有一个SQL表如下：

+---+--------+------------+
|ID | AMOUNT | PRODUCT_ID |
+---+---------------------+
|1  | 100    | 5          |
|2  | 100    | 5          |
|3  | 100    | 5          |
|4  | 100    | 10         |
|5  | 100    | 10         |
|6  | 100    | 10         |
|7  | 100    | 10         | 
+---+--------+------------+

我正在使用codeigniter并期望动态地根据SUM OF AMOUNTS得到PRODUCT_ID。所需的输出是：

sum of product_id 5 = 300
sum of product_id 10 = 400

Answer 1

像GROUP BY一样使用SUM：

SELECT product_id, SUM(amount) AS TotalAmount
FROM tablename
GROUP BY product_id;

Results：

| product_id | TotalAmount |
|------------|-------------|
|          5 |         300 |
|         10 |         400 |

Answer 2

使用GROUP BY和SUM以及COUNT：

SELECT product_id, SUM(amount) AS TotalAmount, COUNT(product_id) as Count
FROM tablename
GROUP BY product_id;

结果：

| product_id | TotalAmount | Count |
|------------|-------------|-------|
|          5 |         300 |    3  |
|         10 |         400 |    4  |

Answer 3

通过使用GROUP_BY product_id和sum

SELECT product_id, SUM(amount) AS TotalAmount
FROM tablename
GROUP BY product_id;