在数据库useri上创建学生选课有关关系模式，并插入相应的数据，实现有关查询。描述学生、课程情况的E-R图如下，请将其转化为用关系数据模型描述的关系模式

在数据库中定义这些关系模式

插入相应的数据，试着插入重复的元组，结果如何？在已建立的关系模式之上（已插入一些数据）建立主键约束，参照约束和用户定义的约束（要求学生年龄不小于14岁，不大于35岁），如果约束不能建立，请分析原因，修改后建立上述约束如果约束建立后，请试着插入重复元组，结果如何？

-Useri in the database to create a class selection on relational model, and insert the appropriate data to achieve the relevant inquiries. Descr iption of students, course conditions as ER diagram, please use the relational data model into a relational schema is described in the definition of these relationships in the database model into the corresponding data, try to insert a duplicate tuple, the result? Established pattern of relations in the above (some data has been inserted) to establish the primary key constraint, referential constraints, and user-defined constraints (requiring students aged not less than 14 years, not more than 35 years of age), if the constraint can not be established, please analyze the reasons , modified to establish the constraints if the constraint is established, try to insert a duplicate tuple, the result?