创建 选课表: 特别注意几个概念:外键,级联 操作 练习: a. 找出的所有选修课程以及成绩; b. 计算所有选修《 Java 程序设计》课程的学生人数; c. 找出选修《 Java 程序设计》课程的成绩的最高分,最低分以及平均分; d. 找出所有选修《 Java 程序设计》课程的学生信息以及成绩; e. 找出既选修《电影欣赏》课程又选修《大学英语写作》课程的学生信息; f. 级联修改,在学生表修改的观察选课表的变化; g. 级联删除,在课程表中删除《电影欣赏》课程观察选课表的变化。
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