Как объединить таблицы с пустыми полями?

Question

[shokw0w]

Всем привет!
Объединил таблицы пропусков и опозданий, данные выходятся по опоздавшим и пропустившим, но также нужны те студенты, которые вообще не опаздывали и не пропускали.

SELECT dbo_grades.gradename,dbo_students.studentname, dbo_days.Day, dbo_absents.absent
FROM dbo_grades INNER JOIN (dbo_students INNER JOIN (dbo_days INNER JOIN dbo_absents ON dbo_days.id_day = dbo_absents.am_day) ON dbo_students.id_students = dbo_absents.studentid) ON dbo_grades.id = dbo_students.gradeid
UNION ALL
SELECT dbo_grades.gradename,dbo_students.studentname, dbo_days.Day,dbo_lates.late
FROM dbo_grades INNER JOIN (dbo_students INNER JOIN (dbo_days INNER JOIN dbo_lates ON dbo_days.id_day = dbo_lates.am_day) ON dbo_students.id_students = dbo_lates.studentid) ON dbo_grades.id = dbo_students.gradeid

UNION ALL SELECT dbo_grades.gradename,dbo_students.studentname, dbo_days.Day,dbo_medical.medical
FROM dbo_grades INNER JOIN (dbo_students INNER JOIN (dbo_days INNER JOIN dbo_medical ON dbo_days.id_day = dbo_medical.am_days) ON dbo_students.id_students = dbo_medical.studentid) ON dbo_grades.id = dbo_students.gradeid;

Answer 1

[Boris Köln]

SELECT ... 
FROM students 
WHERE id_students NOT IN (
   SELECT DISTINCT studentid FROM absents
)

P.S. Почему одно и то же поле называется то id_students, то studentid?