How to filter null value in sql

Question

I have a situation in my sql statement. The statement sql I joined the 3 tables together (Application_Detail, Teacher_Detail and Class_Detail), , and what I used WHEREto filter my table, to find out how many teachers use this app, I found the following result.

As you can see in the first entry, both the teacher-related and the class-related fields are null. I am wondering if there is a way to filter the 1st record and show only the 2,3,4 record? because I only want to show the record if there is any value in the teacherId, teacherName, class or grade column.

   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 

Here is my SQL command

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

:

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 

Answer 2

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 
AND NOT (td.teacherId IS NULL AND class IS NULL AND grade IS NULL)

Answer 3

SELECT *
FROM (
    SELECT td.teacherId AS [TeacherID]
        ,teacherName AS [TeacherName]
        ,applicationName AS [ApplicationName]
        ,class AS [Class]
        ,grade AS [Grade]
    FROM [AppUser_Detail] AS aud
    LEFT JOIN [Teacher_Detail] AS td ON aud.teacherId = td.teacherId
    LEFT JOIN [Application_Detail] AS ad ON aud.applicationId = ad.applicationId
    LEFT JOIN [Class_Detail] AS cd ON aud.classId = cd.classId
    WHERE aud.applicationId = 6
    )
WHERE TeacherID IS NOT NULL
    OR TeacherName IS NOT NULL
    OR Grade IS NOT NULL