获取最大日期行的 SQL 查询

Posted 2023-05-09

【中文标题】获取最大日期行的 SQL 查询

【英文标题】：SQL query to get the maximum dated row

【发布时间】：2020-07-31 12:39:15

【问题描述】：

我有一个查询，它为我的员工提供了不同日期的多行 -

PROCESSSTARTDATE  EMPLOYEENUMBER RUN_ACTION  CURRENTAMOUNT
10-JUL-2020          27             D           10
11-JUL-2020          27             C           10.3
12-JUL-2020          27             F           11.6

11-JUL-2020          28             C           2.8
12-JUL-2020          28             F           2
13-JUL-2020          28             G           11.6

用于上述输出的查询-

Select pa.processstartdate,
paam.assignment_number EMPLOYEENUMBER,
pr.RUN_ACTION RUN_ACTION,
pa.CURRENTAMOUNT
from
per_all_actions pa,
per_all_assignments_m paam,
per_run pr
where pa.action_id = pr.action_id
and paam.assignment_id = pr.assignment_id

我只想要输出中的最大 PROCESSSTARTDATE 行。即

PROCESSSTARTDATE  EMPLOYEENUMBER RUN_ACTION  CURRENTAMOUNT
12-JUL-2020          27             F           11.6
13-JUL-2020          28             G           11.6

怎么做？

【问题讨论】：

你为什么选择不使用正确的、明确的、标准的、可读的JOIN格式？

这是 Oracle 专有的连接语法。

Oracle 在 2001 年的 9i 版本中实现了 ANSI JOIN（标准）格式。但是使用的格式不是专有的，因为其他 RDBMS 也允许使用它。但它在那时已经过时了。

【参考方案1】：

在 Oracle 中，您可以使用带有 keep 关键字的聚合：

Select max(pa.processstartdate) as processstartdate,
       paam.assignment_number as EMPLOYEENUMBER,
       max(pr.RUN_ACTION) keep (dense_rank first order by pa.processstartdate desc) as RUN_ACTION,
       max(pa.CURRENTAMOUNT) keep (dense_rank first order by pa.processstartdate desc) as current_amount
from per_all_actions pa join
     per_run pr
     on pa.action_id = pr.action_id join
     per_all_assignments_m paam
     on paam.assignment_id = pr.assignment_id
group by paam.assignment_number

【参考方案2】：

您可以使用rank 获取每位员工的最新行。附带说明一下，隐式连接（在 from 子句中有多个表）是一种过时的做法，您可能应该改用显式 join 子句：

SELECT processstartdate, employeenumber, run_action, currentamount
FROM   (SELECT pa.processstartdate AS processstartdate,
               paam.assignment_number AS employeenumber,
               pr.run_action AS run_action,
               pa.currentamount AS currentamount,
               RANK() OVER (PARTITION BY paam.assignment_number 
                            ORDER BY processstartdate DESC) AS rk
        FROM   per_all_actions pa
        JOIN   per_run pr ON pa.action_id = pr.action_id
        JOIN   per_all_assignments_m paam ON paam.assignment_id = pr.assignment_id) t
WHERE  rk = 1

【参考方案3】：

使用row_number窗口子句添加伪列，按员工分组并按日期降序排列。

然后将其包装在一个子查询中，您只会看到 row_number=1。

类似：

select *
  from (select pa.processstartdate,
               paam.assignment_number EMPLOYEENUMBER,
               pr.RUN_ACTION RUN_ACTION,
               pa.CURRENTAMOUNT,
               row_number() over(partition by paam.assignment_number order by pa.processstartdate desc) as rn
          from per_all_actions pa, per_all_assignments_m paam, per_run pr
         where pa.action_id = pr.action_id
           and paam.assignment_id = pr.assignment_id) t
 where t.rn = 1