我尝试了mysql和oracle，这个查询是可以的。

SELECT S.sex, count(*) 
FROM student s 
INNER JOIN training T on S.id = T.sid 
GROUP BY S.sex;

结果，女性=1，男性=2

这看起来像您的查询，但是-返回您提到的结果（1个女性，2个男性）。如果可能的话，发布您自己的sql*plus复制/粘贴会话（以我的示例为例），这样我们就可以看到您到底做了什么）。

SQL> with student (id, name, sex) as
  2    (select 1, 'alex', 'm' from dual union
  3     select 2, 'rita', 'f' from dual union
  4     select 3, 'max',  'm' from dual union
  5     select 4, 'steve', 'm' from dual
  6    ),
  7  training (id, sid, course) as
  8    (select 1, 2, 'java' from dual union
  9     select 2, 3, 'c' from dual union
 10     select 3, 1, 'java' from dual
 11    )
 12  select s.sex, count(*)
 13  from student s join training t on t.sid = s.id
 14  group by s.sex;

S   COUNT(*)
- ----------
m          2
f          1

在这里我写了一个代码data:-

SELECT 
    final.ct_sex as sex,count(*) as num
FROM 
    (SELECT tb.sex as ct_sex FROM newschema.mytable AS tb JOIN (SELECT tr.ID,GROUP_CONCAT(tr.skill) as skills FROM newschema.train AS tr GROUP BY tr.ID) AS tp ON tb.ID = tp.ID) as final
group by
    final.ct_sex

使用 exists :

select s.sex, count(*)
from students s
where exists (select 1 from training t where t.sid = s.id);

问题在于 join 它是根据每个学生参加培训的次数来计算的。

如果你唯一想要的是一个简单的按性别统计，为什么不使用

select sex, count(*)
    from student
    group by sex
    order by sex

不知道为什么连接在这里失败，下面的子查询给出了正确的输出。选择sex，count（*）from salary where salary.id in（select sid from training）group by salary.sex；