分组时如何将条件限制为 CASE 中的数据子集？

Question

假设 table:

| ID | Customer | Agent    | Event     | Date       |
|====|==========|==========|===========|============|
| 01 | Steve    | Jerry    | Booked    | 2019-01-01 |
| 02 | Steve    | Jerry    | Canceled  | 2019-01-13 |
| 03 | Steve    | Rusty    | Booked    | 2019-01-16 |
| 04 | Carla    | JSnow    | Booked    | 2019-01-04 |
| 05 | Carla    | JSnow    | Resched   | 2019-01-16 |

我有一个查询，将事件列表分组到它们的所有者中，检测第一个预订日期，并记录第一个预订的代理：

SELECT 
    Customer,
    FIRST_VALUE(Agent),
    MIN(CASE WHEN Event = 'Booked' THEN Date END) as BookDate,
    MIN(CASE WHEN Event = 'Canceled' THEN Date END) as CancelDate
FROM Events
GROUP BY Customer

// produces:
| Customer | Agent    | BookDate   | CancelDate |
|==========|==========|============|============|
| Steve    | Jerry    | 2019-01-01 | 2019-01-13 |
| Carla    | JSnow    | 2019-01-04 | NULL       |

我正在尝试添加一个 "Booking Agent After Cancel" 列，使其看起来像这样：

| Customer | Agent    | BookDate   | CancelDate | Agent2   |
|==========|==========|============|============|==========|
| Steve    | Jerry    | 2019-01-01 | 2019-01-13 | Rusty    |
| Carla    | JSnow    | 2019-01-04 | NULL       | NULL     |

我不知道如何将代理名称的聚合限制为仅包含 'Booked' 日期超过 'Canceled' 日期（如果存在）的事件。

Answer 1

我认为没有任何方法可以仅通过聚合来做到这一点。但是在子查询中添加 LAG() 可以为您提供所需的信息：

SELECT Customer, FIRST_VALUE(Agent),
       MIN(CASE WHEN Event = 'Booked' THEN Date END) as BookDate,
       MIN(CASE WHEN Event = 'Canceled' THEN Date END) as CancelDate,
       MIN(CASE WHEN prev_event = 'Canceled' THEN Agent END) as Agent2
FROM (SELECT e.*, 
             LAG(Event) OVER (PARTITION BY Customer ORDER BY Date) as prev_event
      FROM Events e
     ) e
GROUP BY Customer;

分组时如何将条件限制为 CASE 中的数据子集？

How do I limit a condition to a subset of data in a CASE when grouping?

sql

snowflake-cloud-data-platform