设置score表的sid列为外键，关联stu表的sid列，可以使用以下哪条命令实现。 A: alter table stu add constraint fk_sid foreign key(sid) references stu(sid); B: alter table stu add constraint fk_sid foreign key(sid) references score(sid); C: alter table score add constraint fk_sid foreign key(sid) references sore(sid); D: alter table score add constraint fk_sid foreign key(sid) references stu(sid);

查询选修了2门课程以上的学生学号（） A: select sid,count(*) from sc group by sid having count(*)>=2 B: select sid,count(*) from sc group by sid where count(*)>=2 C: select sid,count(*) from sc where count(*)>=2 group by sid D: select sid,count(*) from sc group by cid having count(*)>=2

按照学号进行分组，统计学生的平均成绩（） A: select sid, avg(grade) from student group by cid B: select sid, avg(grade) from student group by sid C: select sid, avg(grade) from sc group by sid D: select sid, avg(grade) from sc group by cid

DR设备的安装缩光器照射野和指示灯照射野应一致，允许误差值为（） A: <1%SID B: <2%SID C: <3%SID D: <5%SID

在查询学生信息表Student_info数据时,为学号列Sid定义别名为学号,以下选项正确的是______。A.()select()Sid()as()学号()from()Student_info()B.()select()学号()Sid()from()Student_info()C.()select()学号()as()Sid()from()Student_info()D.()select()Sid=学号()from()Student_info

完成下面的Person类封装填空。 ________ com.softfz; ________ class Person { _______ int sid; _______ String sname; _______ int getSid() { return sid; } _______ void setSid(int sid) { this.sid = sid; } _______ String getSname() { return sname; } _______ void setSname(String sname) { this.sname = sname; } }

何谓SID码？

各系列产品重点考虑指标，其中小猪料考虑的重点营养指标是（） A: 功能性、净能、SID氨基酸 B: 蛋白、SID赖氨酸 C: 净能、SID氨基酸 D: 纤维、FCHO、ICHO、净能、SID氨基酸

按照学号进行分组，统计学生的平均成绩，且平均分按降序排列 A: select sid, avg(grade) from sc group by sid order by avg(grade) desc B: select sid, avg(grade) from sc group by cid order by avg(grade) desc C: select sid, avg(grade) from student group by sid order by avg(grade) desc D: select sid, avg(grade) from student group by cid order by avg(grade)

以下创建视图的语句中,正确的是 A: CREATE st_view AS SELECT sid,sname,ssex FROM stu B: CREATE VIEW st_view SELECT sid,sname,ssex FROM stu C: CREATE VIEW st_view AS sid,sname,ssex FROM stu D: CREATE VIEW st_view AS SELECT sid,sname,ssex FROM stu