Question

我有表grades：

id | student_id | grade
-----------------------
1  | 1          | 4
2  | 1          | 5
3  | 2          | 3

我想要一个返回student_id和平均grade的查询：

student_id | avg_grade
----------------------
1          | 4.5
2          | 3

什么查询会这样做？

Answer 1

SQL AVG()函数执行此操作：

SELECT student_id, AVG(grade) as avg_grade
FROM grades
GROUP BY student_id