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后缀 -If 可以附加到任何聚合函数的名称之后。此时,聚合函数会接受一个额外的参数,即条件。

func.sum_if(<column>, <cond>)
func.sum_if(table.amount, table.status=='Completed').alias('total_amount_completed')
| total_amount_completed |
|------------------------|
| 270.0 |
SUM_IF(<column>, <cond>)

创建表并插入示例数据

CREATE TABLE order_data (
id INT,
customer_id INT,
amount FLOAT,
status VARCHAR
);
INSERT INTO order_data (id, customer_id, amount, status)
VALUES (1, 1, 100, 'Completed'),
(2, 2, 50, 'Completed'),
(3, 3, 80, 'Cancelled'),
(4, 4, 120, 'Completed'),
(5, 5, 75, 'Cancelled');

查询演示:计算已完成订单的总金额

SELECT SUM_IF(amount, status = 'Completed') AS total_amount_completed
FROM order_data;

结果

| total_amount_completed |
|------------------------|
| 270.0 |