Sql 是否按最长日期的计数分组显示结果？

我有下面的样本数据，我需要显示结果，按最大日期分组计数

REQUEST_NUMBER  ASSIGNED_GROUP  LAST_MODIFIED_DATE
001             GROUP A         
001             GROUP B         2/2/2018
002             GROUP A         
002             GROUP B         2/2/2018
002             GROUP C         2/3/2018
003             GROUP B         

我的预期结果需要显示为组的计数，最大值为上次修改日期，如下所示：

ASSIGNED_GROUP  TOTAL_COUNT
GROUP B         2
GROUP C         1

在我上面的例子中，001最后分配给B组，002最后分配给C组，003是仅有1条记录，最后修改日期为空，因此保留在B组

到目前为止，我只尝试了一个结果，但没有得到正确的结果：

SELECT request_number, ASSIGNED_GROUP_NAME
FROM (
    SELECT ROW_NUMBER() OVER (PARTITION BY request_number ORDER BY request_number) RNUM,
           request_number, ASSIGNED_GROUP_NAME
    FROM WORK_DETAIL
    WHERE request_number = '3458112'
    )
WHERE MAX(last_modified_date)
ORDER BY ASSIGNED_GROUP_NAME

你可以使用分组方式

---

像这样的东西可能有用

    SELECT ASSIGNED_GROUP, COUNT(ASSIGNED_GROUP), MAX(LAST_MODIFIED_DATE) FROM YourTable
    GROUP BY ASSIGNED_GROUP

---

您可以将ajoin与子查询一起使用，该子查询具有指定的最大日期组

select a.ASSIGNED_GROUP, count(*)
from my_table  a
inner join(

  select ASSIGNED_GROUP,  max(LAST_MODIFIED_DATE) as max_date
  from my_table 
  where LAST_MODIFIED_DATE is not null
  group by ASSIGNED_GROUP

) t on t.max_date = a.LAST_MODIFIED_DATE and t.ASSIGNED_GROUP = a.ASSIGNED_GROUP
group by a.assigned_group

---

好吧，你们试过什么了？这不考虑maxlast修改日期前的记录

select a.ASSIGNED_GROUP, count(*)
from my_table  a
inner join(

  select ASSIGNED_GROUP,  max(LAST_MODIFIED_DATE) as max_date
  from my_table 
  where LAST_MODIFIED_DATE is not null
  group by ASSIGNED_GROUP

) t on t.max_date = a.LAST_MODIFIED_DATE and t.ASSIGNED_GROUP = a.ASSIGNED_GROUP
group by a.assigned_group