确定最大计数最高的会话

Question

我有一个包含以下字段的表：

• 访问 ID
• CPCCID
• 日期
• Time_IN
• 超时
• 课程
• LA_CPCCID

有 3 个会话，9-12、12-3 和 3-6。

我需要一个脚本来计算访问者最多的会话。

我有这个附加的代码，它将确定会话 # 和最大计数：

select Time_In ,
CASE
When cast(Time_In as time) >'12:00:00' and cast(Time_In as time) <='15:00:00' /* and date = cast(GETDATE() as date)*/ then 'Session 2' 

when cast(Time_In as time) >'3:00:00' and cast(Time_In as time)<= '6:00:00' /*and date = cast(GETDATE() as date)*/ then 'Session 3'

else 'Session 1'
end "sessions"
from Lab_Visits2;


select max(visit.cnt) 
from
(select course, count(course) cnt
from Lab_Visits2
group by Course) visit;

Answer 1

如果我正确理解了您的问题，您希望返回按会话/课程分组的访问者最多的会话和课程。如果是这样，这将使用几个common-table-expressions 来选择会话，然后按会话和课程分组以获取访问者数量。最后，使用row_number 建立最大值：

with cte as (
  select 
      case
        when cast(Time_In as time) >'12:00:00' and cast(Time_In as time) <='15:00:00' /* and date = cast(GETDATE() as date)*/ then 'Session 2' 
        when cast(Time_In as time) >'3:00:00' and cast(Time_In as time)<= '6:00:00' /*and date = cast(GETDATE() as date)*/ then 'Session 3'
        else 'Session 1'
      end session,
      course
    from Lab_Visits2
  ), ctecnt as (
  select session, course, count(*) cnt
  from cte
  group by session, course
)
select session, course, cnt
from (
  select session, course, cnt, row_number() over (order by cnt desc) rn
  from ctecnt
  ) t
where rn = 1

• SQL Fiddle Demo

如果我误解了，而您只想要最高计数的会话（当然不管），那么只需从所有查询中删除课程字段。