SELECT case when Ssex=‘男‘ then ‘男生人数‘ ELSE ‘女生人数‘ END  ‘男女情况‘,count(1) ‘人数‘  
 FROM student
 GROUP BY
case when Ssex=‘男‘ then ‘男生人数‘ ELSE ‘女生人数‘ END

SELECT count(Ssex) as 男生人数 FROM student WHERE Ssex=‘男‘;
SELECT count(Ssex) as 女生人数 FROM student WHERE Ssex=‘女‘;

select 
sum(case when Ssex = ‘男‘ then 1 else 0 end) 男生人数,
sum(case when Ssex = ‘女‘ then 1 else 0 end) 女生人数 
from student