select students.*
from students, grades
where students.sno=grades.sno
AND grades.cno <> ’B2’
上面的查询方式是错误的,正确方式见下方:
select * from students
where not exists (select * from grades
where grades.sno=students.sno AND cno='B2')
这两中方法都正确吗
select students.*
from students, grades
where students.sno=grades.sno
AND grades.cno <> ’B2’
上面的查询方式是错误的,正确方式见下方:
select * from students
where not exists (select * from grades
where grades.sno=students.sno AND cno='B2')
这两中方法都正确吗
有谁能告诉我上面那种方法为什么不对