Question

我正在尝试在一列上使用case语句，并在条件满足时计算另一列的聚合。

我正在查询的示例数据表（例如酒店）如下所示：

|  date  | customer_name | customer_id | expense_type | billed_amount |
|  08-02 |   John Doe    |      1      |   personal   |     120.00    |
|  08-03 |   John Doe    |      1      |   personal   |      80.00    |
|  08-04 |   John Doe    |      1      |   corporate  |     205.00    |
|  08-02 |   Adam Smith  |      2      |   corporate  |     400.00    |
|  08-03 |   Adam Smith  |      2      |   personal   |     300.00    |
|  08-06 |   Adam Smith  |      2      |   corporate  |     150.00    |

下面是我写的SQL查询：

Select
    customer_name
    , customer_id
    , case when expense_type = 'personal' then sum(billed_amount) else 0 end as personal_bill
    , case when expense_type = 'corporate' then sum(billed_amount) else 0 end as corporate_bill
From payments
Where date > '08-01'
Group by 1, 2

我得到的错误信息是：

Column "expense_type" must appear in the GROUP BY clause or be used in an aggregate function

当我尝试对第3列进行分组时（以及1和2），我收到此错误消息：

Aggregates not allowed in GROUP BY clause

最后，下面说明了所需的结果表：

| customer name | customer_id | personal_bill | corporate_bill |
|   John Doe    |      1      |     200.00    |     205.00     |
|   Adam Smith  |      2      |     300.00    |     550.00     |

我能想到的一个解决方案是创建两个不同的子查询来约束Where部分中的“expense_type”（即，其中expense_type ='personal'），然后在主查询中查询它们，但这是很多类似的代码一线差异。能帮我写一下这个查询吗？谢谢！

Answer 1

求和整个CASE表达式：

select
    customer_name,
    customer_id,
    sum(case when customer_type = 'personal'
             then billed_amount else 0 end) as personal_bill
    sum(case when customer_type = 'corporate'
             then billed_amount else 0 end) as corporate_bill
from payments
where date > '08-01'
group by 1, 2

Answer 2

试试这个： -

Select MIN(customer_name) AS customer_name, customer_id,
       SUM(case when expense_type = 'personal' then billed_amount::double precision else 0 end) as personal_bill, 
       SUM(case when expense_type = 'corporate' then billed_amount::double precision else 0 end) as corporate_bill
From payments
Where date > '08-01'
Group by customer_id
ORDER BY customer_id;

Answer 3

使用filter：

select
    customer_name,
    customer_id,
    sum(billed_amount) filter (where expense_type = 'personal') as personal_bill,
    sum(billed_amount) filter (where expense_type = 'corporate') as corporate_bill
from payments
where date > '08-01'
group by 1, 2

 customer_name | customer_id | personal_bill | corporate_bill 
---------------+-------------+---------------+----------------
 Adam Smith    |           2 |        300.00 |         550.00
 John Doe      |           1 |        200.00 |         205.00
(2 rows)

在一列上使用CASE语句并计算另一列

3 个答案: