SQL：使用max / min聚合函数和相关记录

Question

+-------------------------+
| id  date value comments |
+-------------------------+
| 1   d1    10    c1      |
| 1   d2    20    c2      |
| 1   d3    30    c3      |
| 2   d7    70    c4      |
+-------------------------+

想要编写一个SQL来创建如下所示的展平表：

id | max_value | date_of_max_value | min_value | date_of_min_value

Answer 1

大多数数据库都支持窗口功能，例如row_number()。这让您可以使用条件聚合来解决这个问题：

select id, max(value) as max_value,
       max(case when seqnum_desc = 1 then date end) as date_max_value,
       min(value) as min_value,
       max(case when seqnum_asc = 1 then date end) as date_min_value
from (select t.*,
             row_number() over (partition by id order by value asc) as seqnum_asc,
             row_number() over (partition by id order by value desc) as seqnum_desc
      from t
     ) t
group by id;