一道查询的题目

Question

显示计算机系年龄在23岁以上的同学姓名，性别；有student,sc,source,department表，年龄需要计算，只告诉出生年月，我编的如下:(但就是筛选不出23岁的，总是把全部的都显示出来了)
declare @stu_datetime int
declare @diffyear int
select datediff(year,student_birthday,getdate()),
student_name,
student_gender=(case when student_gender= 0 then '男' when student_gender=1 then'女' end),
student_birthday=(datediff(year,student_birthday,getdate()))
from student
where student_birthday>23

Answer 1

select name
from student
where datediff(year,birthday,getdate())>23

Answer 2

declare @stu_datetime int
declare @diffyear int
select datediff(year,student_birthday,getdate()),
student_name,
student_gender=(case when student_gender= 0 then '男' when student_gender=1 then'女' end),
student_birthday=(datediff(year,student_birthday,getdate()))
from student
--where student_birthday>23
where datediff(year,student_birthday,getdate())>23