我有一个数据结构,学生和小组之间有多对多的关系.我有三张桌子
students: id,name
groups: id,name
students_groups: student_id,group_id
如何仅选择不在特定组中的学生(例如group.id = 1)?
select * from students where not exists (select students.* from students left join students_groups on students_groups.student_id = student.id where students_groups.group_id = 1);
我该怎么查询?提前多了!
编辑
好吧,似乎以下两个终于有效……任何人都可以解释为什么我不需要加入表来工作?
select * from students where not exists (select * from students_groups where students_groups.student_id = student.id and student_groups.group_id = 1); select * from students where id not in (select student_id from students_groups where group_id = 1);
解决方法
使用NOT IN应该可以正常工作:
SELECT * FROM Students WHERE Id NOT IN ( SELECT Student_Id FROM Students_Groups WHERE Group_Id = 1)