根据 Results/ID 计算最终结果

Question

对于 Table T1

+----------+-----------+-----------------+
| PersonID |   Date    |   Employment    |
+----------+-----------+-----------------+
|        1 | 2/28/2017 | Stayed the same |
|        1 | 4/21/2017 | Stayed the same |
|        1 | 5/18/2017 | Stayed the same |
|        2 | 3/7/2017  | Improved        |
|        2 | 4/1/2017  | Stayed the same |
|        2 | 6/1/2017  | Stayed the same |
|        3 | 3/28/2016 | Improved        |
|        3 | 5/4/2016  | Improved        |
|        3 | 4/19/2017 | Worsened        |
|        4 | 5/19/2016 | Worsened        |
|        4 | 2/16/2017 | Improved        |
+----------+-----------+-----------------+

我正在尝试根据相对于先前结果的最新 result/person 在 Employment/PersonID 字段上计算 Final Result 字段分区。 Final Result:

背后的逻辑解释了我的意思

对于每个人，

1. 如果所有results/person都保持不变，那么只应该final 该人的结果是 "Stayed the same"

2. 如果Worsened/Improved 在一个人的结果集中，最终结果应该是 该人的最新 Worsened/Improved 结果，与 W/I 结果之后的 "Stayed the same" 无关。

例如：

• 第 1 个人最终结果 -> 与 (1) 相同
• 第 2 个人最终结果 -> 根据 (2)
进行了改进
• 人 3 最终结果 -> 根据 (2)
恶化
• 第 4 个人最终结果 -> 根据 (2)
进行了改进

想要的结果：

+----------+-----------------+
| PersonID |  Final Result   |
+----------+-----------------+
|        1 | Stayed the same |
|        2 | Improved        |
|        3 | Worsened        |
|        4 | Improved        |
+----------+-----------------+

我知道这可能涉及 Window 函数或子查询，但我正在努力编写代码。

Answer 1

嗯。这是一个优先查询。这听起来像 row_number() 要求：

select t1.personid, t1.employment
from (select t1.*,
             row_number() over (partition by personid
                                order by (case when employment <> 'Stayed the same' then 1 else 2 end),
                                         date desc
                               ) as seqnum
      from t1
     ) t1
where seqnum = 1;