从满足条件的表中选择而不是满足条件的表

Question

我有3张桌子：

Students
(student_id, name, group, year, specialization)

Scolarships
(scolarship_id, name, description, duration)

Applicants
(student_id, scolarship_id)

我需要选择所有已申请奖学金的学生id=2且尚未申请id=4

的奖学金

到目前为止，我有这个问题：

select students.name, students.group, students.specialization
from applicants ap
inner join students on students.id = ap.student_id
inner join scolarships on scolarships.scolarship_id = ap.scolarship_id
where ap.scolarship_id = 2;

这将选择所有已申请奖学金且id = 2的学生。

如何添加申请奖学金2的条件但尚未申请奖学金4？

Answer 1

试试这个

select students.name, students.group, students.specialization
from applicants ap
inner join students on students.id = ap.student_id
inner join scolarships on scolarships.scolarship_id = ap.scolarship_id
where ap.scolarship_id = 2 and not exists(select * from applicants as t1
where t1.student_id = students.student_id and t1.scolarship_id = 4)

Answer 2

您可以使用environ内容作为

not exists