mysql - SQL 查询 - 打印同一行中一个表的最小值和最大值

Question

我需要一些关于 SQL 查询的帮助。

我有一个表格，其格式和数据如下所示:

id | applicant_id | application_status | status_time
1  | 1234         | received           | 2013-05-06 15:00:00
1  | 1234         | pending            | 2013-05-06 15:30:00
1  | 1234         | approved           | 2013-05-06 16:00:00

我需要解决的问题必须打印以下内容:

applicant_id | initial_status | initial_time        | current_status | current_status_time
1234         | received       | 2013-05-06 15:00:00 | approved       | 2013-05-06 16:00:00

我怎样才能完成这样的事情，最好只使用联接而不使用嵌套选择？

Answer 1

一般来说，解决此问题的最佳方法是使用 row_number() 函数。但是，这需要嵌套选择:

select t.applicant_id,
       max(case when seqnum_asc = 1 then status end) as initial_status,
       max(case when seqnum_asc = 1 then status_time end) as initial_time,
       max(case when seqnum_desc = 1 then status end) as current_status,
       max(case when seqnum_desc = 1 then status_time end) as current_time
from (select t.*,
             row_number() over (partition by applicant_id order by status_time) as seqnum_asc,
             row_number() over (partition by applicant_id order by status_time desc) as seqnum_desc
      from t
     ) t
group by t.applicant_id;

如果您的数据库不支持row_number()，我建议使用相关子查询，以提高可读性。但这些也是嵌套的。这是 MySQL 中满足您要求的解决方案:

select t.applicant_id,
       substring_index(group_concat(status) separator ',' order by status_time), ',', 1) as initial_status,
       min(status_time) as initial_time,
       substring_index(group_concat(status) separator ',' order by status_time desc), ',', 1) as current_status,
       max(status_time) as current_time
from t
group by t.applicant_id;