c# - sql中如何过滤空值

Question

我的sql语句有一个情况。在此 sql 语句中，我将 3 个表连接在一起(Application_Detail、Teacher_Detail 和 Class_Detail)，然后我使用 WHERE 来过滤我的表以找出有多少老师使用了这个应用程序，我发现了以下结果。

在第一条记录中可以看到，teacher related 和 class related 字段都是空的。我想知道有没有办法过滤掉第 1 条记录，只显示第 2、3、4 条记录？因为我只想在 teacherId、teacherName、class 或 grade 列中有一些值时显示记录。

   teacherId teacherName   applicationName  class   grade
1. NULL      NULL         Excel            NULL     NULL
2. 5         NULL         Excel            NULL     NULL
3. NULL      NULL         Excel            A        6
4  NULL      NULL         Excel            B        2 

这是我的 SQL 命令

SELECT
   td.teacherId,
   teacherName,
   applicationName,
   class,
   grade
FROM
   [AppUser_Detail] as aud
LEFT OUTER JOIN [Teacher_Detail] as td ON aud.teacherId = td.teacherId
LEFT OUTER JOIN [Application_Detail] as ad ON aud.applicationId = ad.applicationId
LEFT OUTER JOIN [Class_Detail] as cd ON aud.classId = cd.classId
WHERE
aud.applicationId = 6 //I filter if my application Id is 6 

Answer 1

试试这个:

SELECT
   td.teacherId,
   teacherName,
   applicationName,
   class,
   grade
FROM
   [AppUser_Detail] as aud
LEFT OUTER JOIN [Teacher_Detail] as td ON aud.teacherId = td.teacherId
LEFT OUTER JOIN [Application_Detail] as ad ON aud.applicationId = ad.applicationId
LEFT OUTER JOIN [Class_Detail] as cd ON aud.classId = cd.classId
WHERE
td.teacherId is not null OR class is not null OR grade is not null