计数（不同）超过（分区依据）sql 服务器 2016

Question

我有一个 table 如下所示

class_no	student_id	subject_name
1	636	Physics
1	636	Chemistry
1	637	Maths
1	638	German
1	639	Physics

Create table #T_Test(
     class_no int
     ,student_id int
     ,subject_name nvarchar(25)
);
Insert into #T_Test ([class_no],[student_id],[subject_name]) values
(1,636,'Physics'),
(1,636,'Chemistry'),
(1,637,'Maths'),
(1,638,'German'),
(1,639,'Physics')

我想得到不同 student_id 的计数，还要计算 grouped_by subject_names

class_no	subject_name	total_subjects	total_students
1	Physics	2	4
1	Chemistry	1	4
1	Maths	1	4
1	German	1	4
1	Physics	1	4

下面是我到目前为止所做的，我怎样才能得到结果集中包含的非重复计数（student_id）

SELECT  DISTINCT t.class_no
        ,t.subject_name
        ,count(*) total_subject
FROM        #T_Test t
WHERE       t.class_no = 1
GROUP BY    t.class_no,subject_name

Answer 1

我认为您正在寻找这个查询：

SELECT DISTINCT 
    t.class_no,
    t.subject_name,
    total_subjects = Count(t.subject_name) OVER(Partition By t.class_no, t.subject_name),
    total_students = (SELECT COUNT(Distinct [student_id]) FROM #T_Test)
FROM    #T_Test t
WHERE   t.class_no = 1

Answer 2

通过使用这个 dense_rank 小技巧，无需多次点击 table 即可获得科目总数和不同的学生人数：

with s as (
    select class_no, subject_name,
    Dense_Rank() over (partition by class_no order by student_id) + 
    Dense_rank() over (partition by class_no order by student_id desc) - 1 Students
    from #T_Test
)
select class_no, subject_name,  
  Count(*) Total_Subjects, 
  Max(students) Total_Students
from s
group by class_no, subject_name

计数（不同）超过（分区依据）sql 服务器 2016

Count(distinct) over (partition by) sql server 2016

sql

sql-server

sql-server-2016