Question

该数据库具有模式学生（名称TEXT，math_grade INTEGER，physics_grade INTEGER）。我想选择所有学生的姓名，并选择一个列，如果有另一个学生的数学和物理成绩相同，则该条目为1，否则为0。如何编写查询？

Answer 1

嗯。。。我在考虑case和exists：

select s.*,
       (case when exists (select 1
                          from students s2
                          where s2.math_grade = s.math_grade and
                                s2.physics_grade = s.physics_grade and
                                s2.name <> s.name
                          )
             then 1 else 0
        end) as is_same_flag
from students s;

Answer 2

自我加入：

select s1.name, case when max(s2.name) is not null then 1 else 0 end
from students s1
left join students s2 on s2.name <> s1.name and s2.math_grade=s1.math_grade and s2.physics_grade=s1.physics_grade
group by s1.name

返回值进行比较

2 个答案: