我目前正在使用SQL Server 2008.我有多个记录,学生在同一课程中注册,但有些记录具有相同的开始日期和空值或结束日期的实际日期。如果同一个学生的开始日期相同,我试图获取空值的记录。系统中的数据还包含具有开始和结束日期的记录,但我打算保留这些记录。我已经尝试了下面的查询,但它没有给我任何结果。有没有办法实现这个目标?任何帮助,将不胜感激。
SELECT DISTINCT
t1.*
FROM Enrolled_students t1
JOIN Enrolled_students t2
ON t1.studentid = t2.studentid
AND t1.program_enrolled = t2.program_enrolled
AND t1.startdate = t2.stardate
AND t1.enddate <> t2.enddate
数据
StudentID program StartDate enddate_Date
267342 Science 2016-09-19 00:00:00.000 NULL
267342 science 2016-09-19 00:00:00.000 2017-01-17 00:00:00.000
435359 math 2017-05-18 00:00:00.000 2017-08-29 00:00:00.000
290332 Lab 2014-02-11 00:00:00.000 NULL
结果
StudentID program startDate end_Date
267342 Science 2016-09-19 00:00:00.000 NULL
435359 math 2017-05-18 00:00:00.000 2017-08-29 00:00:00.000
290332 Lab 2014-02-11 00:00:00.000 NULL
运行以下SQL。这将返回带有结束日期的学生记录,该结果日期在同一个表中为同一学生+课程+开始日期组合中的另一个条目,在结束日期为NULL
SELECT
*
FROM Enrolled_students
WHERE enddate_Date IS NOT NULL
AND EXISTS
(
SELECT
1
FROM Enrolled_students ES
WHERE ES.StudentID = Enrolled_students.StudentID
AND ES.Program = Enrolled_students.Program
AND ES.StartDate = Enrolled_students.StartDate
AND ES.enddate_Date IS NULL
)
你可以试试这个。
SELECT * FROM Enrolled_students E1
WHERE NOT EXISTS
( SELECT * FROM Enrolled_students E2
WHERE E1.StudentID = E2.StudentID
AND E1.enddate_Date IS NOT NULL
AND E2.enddate_Date IS NULL )
结果:
StudentID program StartDate enddate_Date
----------- -------------------- ----------------------- -----------------------
267342 Science 2016-09-19 00:00:00.000 NULL
435359 math 2017-05-18 00:00:00.000 2017-08-29 00:00:00.000
290332 Lab 2014-02-11 00:00:00.000 NULL