23 - 每位教师所教授的科目种类的数量（高频 SQL 50 题基础版)

23 - 每位教师所教授的科目种类的数量

• 考点： 排序和分组
  
  
  

select
    teacher_id,count(distinct subject_id) cnt 
from
    Teacher 
group by
    teacher_id;