ABAP : Iner join with Internal table

TABLES: ZPAT_STUDENT,ZPAT_SUBJECT.
DATA it_student type zpat_student OCCURS 0 WITH HEADER LINE.
DATA it_subject type zpat_subject OCCURS 0 with HEADER LINE.
*DATA: st_name type zpat_student-name,
*      st_grade type zpat_student-grade,
*      st_subject type zpat_subject-subject.
write: 'name',20 'grade',30 'subject'.
SELECT a~name a~grade b~subject
  into (it_student-name, it_student-grade, it_subject-subject)
  from ZPAT_STUDENT as a INNER JOIN zpat_subject as b
  on a~grade = b~grade.
*  WRITE: / st_name, 20 st_grade, 30 st_subject.
  WRITE: / it_student-name, 20 it_student-grade ,30 it_subject-subject.
ENDSELECT.