写一句SQL语句找出没有Student的Class
select class.name from class left join student on class.id = student.c_id where student.name is null;
对于Class里面的totalScore，计算规则是此Class下所有学生score的总和，写一句SQL实现全表totalScore的更新
update class set TOTAL_SCONE = (select sum(SCORE) from student where class.id=student.c_id)
如果class里有错误的totalScore记录（不瞒住上面计算逻辑的），写一句SQL查找出所有totalScore记录不正确的Class。
select * from class where class.total_scone <> (select sum(SCORE) from student where class.id=student.c_id)
在之前的某个方法中输出了一个学生集合Collection<Student>，现希望在代码中对其学生名称（name）进行排序（补充：学生没有重名的）
class TestSort:public class TestSort{ public static void main(String args[]){ TestObj obj1 = new TestObj("chensheng1","n"); TestObj obj2 = new TestObj("chensheng2","n"); TestObj obj3 = new TestObj("chensheng3","s"); TestObj obj4 = new TestObj("chensheng4","n"); TestObj obj5 = new TestObj("chensheng5","s"); TestObj obj6 = new TestObj("chensheng6","s"); Collection<TestObj> list = new ArrayList<TestObj>(); list.add(obj1); list.add(obj3); list.add(obj4); list.add(obj2); list.add(obj6); list.add(obj5); Collections.sort((ArrayList)list); for(TestObj k : list){ System.out.println(k.getName() +"--"+k.getSex()); } }}class TestObj:public class TestObj implements Comparable { private String name; private String sex; public TestObj(String name,String sex){ this.name = name; this.sex = sex; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } @Override public String toString() { return "name: "+getName() +" sex: "+getSex(); } @Override public int compareTo(Object o) { return this.name.compareTo(((TestObj)o).name); }}