Question

我有一张桌子出勤（SessionId，StudentId，IfPresent）

S1, Stu001, 1 
S1, Stu002, 1 
S1, Stu003, 1 
S1, Stu004, 1 
S1, Stu005, 1 
S2, Stu001, 1 
S2, Stu002, 0 
S2, Stu065, 1 
S3, Stu003, 0 
.
.
.

主要收集有关分配到特定课程并参加课程的学生的信息。

我想要的是这样的报告

Attendance_report（SessionId，学生总数，出勤率）

S13, 20, 18 
S15, 20, 17 
S56, 40, 28

出勤将在where子句中使用IfPresent = 1进行计数学生总数将来自一个没有任何where子句的计数

Answer 1

试试这个

Select SessionId, count(*) as [Total Students],
sum(case when IfPresent = 1 then 1 else 0 end) as Attendance 
from Attendance_report
group by SessionId

Answer 2

按SessionId分组，以便每个会话获得一个结果行并构建聚合（在您的情况下，这是一个简单的计数和总和）：

select
  sessionid,
  count(*) as total_students,
  sum(ifpresent) as attendance
from attendance
group by sessionid;

Answer 3

BEGIN TRAN

Create Table #Attandance (Session_ID NVARCHAR(10),StudentId NVARCHAR(20), IfPresent INT )
INSERT INTO #Attandance
SELECT 'S1', 'Stu001', 1  UNION ALL
SELECT 'S1', 'Stu002', 1 UNION ALL
SELECT 'S1', 'Stu003', 1 UNION ALL
SELECT 'S1', 'Stu004', 1 UNION ALL
SELECT 'S1', 'Stu005', 1 UNION ALL
SELECT 'S2', 'Stu001', 1 UNION ALL
SELECT 'S2', 'Stu002', 0 UNION ALL
SELECT 'S2', 'Stu065', 1 UNION ALL
SELECT 'S3', 'Stu003', 0 


SELECT Session_ID,COUNT(*)[Total Students], 
SUM(IfPresent)from #Attandance
GROUP BY Session_ID

ROLLBACK TRAN

如何使用count和group by两列，其中不同的子句在哪里

3 个答案: