LC 2356每位教师所教授的科目种类的数量Number of Unique Subjects Taught by Each Teacher　简单

Teacher 表每行是教师在某系教授某科目；统计每位教师教授的不同科目数量。

思路 GROUP BY + COUNT(DISTINCT subject_id)。

SELECT teacher_id,
       COUNT(DISTINCT subject_id) AS cnt
FROM Teacher
GROUP BY teacher_id;

数据表：Teacher　·　关键字：统计每位教师教授的不同科目数量