用SQL语句查询一个特定老师学生中男生女生各多少人

一 表结构

学生表

教师表

关系表

SQL语句

select 
count(case when student.sex = 1 then student.sex end) as 'man',
count(case when student.sex = 0 then student.sex end) as 'woman'
from student where student.studentid in 
(
select studentId from relation where relation.teacherId 
= (select teacher.teacherId from teacher where name = "Tom")
)

结果

涉及知识

1. in 操作符
2. where 条件
3. count() 统计
4. case when ->MySQL 高级函数 菜鸟教程有详细内容 https://www.runoob.com/mysql/mysql-functions.html