正文
难度中等
SQL架构
表：Enrollments
+---------------+---------+ | Column Name | Type | +---------------+---------+ | student_id | int | | course_id | int | | grade | int | +---------------+---------+ (student_id, course_id) 是该表的主键。
Enrollments 表： +------------+-------------------+ | student_id | course_id | grade | +------------+-----------+-------+ | 2 | 2 | 95 | | 2 | 3 | 95 | | 1 | 1 | 90 | | 1 | 2 | 99 | | 3 | 1 | 80 | | 3 | 2 | 75 | | 3 | 3 | 82 | +------------+-----------+-------+ Result 表： +------------+-------------------+ | student_id | course_id | grade | +------------+-----------+-------+ | 1 | 2 | 99 | | 2 | 2 | 95 | | 3 | 3 | 82 | +------------+-----------+-------+
提示：开窗
