1、表：table1(FId,Fclass,Fscore),用最高效最简单的SQL列出各班成绩最高的列表，显示班级，成绩两个字段。

select fclass,max(fscore) from table1 group by fclass,fid

2、有一个表table1有两个字段FID，Fno，字都非空，写一个SQL语句列出该表中一个FID对应多个不同的Fno的纪录。
类如：
101a1001
101a1001
102a1002
102a1003
103a1004
104a1005
104a1006
105a1007
105a1007
105a1007
结果：
102a1002
102a1003
104a1005
104a1006

select t2.* from table1 t1, table1 t2 where t1.fid = t2.fid and t1.fno t2.fno;

3、有员工表empinfo
(
Fempno varchar2(10) not null pk,
Fempname varchar2(20) not null,
Fage number not null,
Fsalary number not null
);
假如数据量很大约1000万条；写一个你认为最高效的SQL，用一个SQL计算以下四种人：
fsalary>9999 and fage > 35
fsalary>9999 and fage < 35
fsalary 35
fsalary 9999 and fage > 35
then 1
else 0end) as "fsalary>9999_fage>35",
sum(case when fsalary > 9999 and fage < 35
then 1
else 0
end) as "fsalary>9999_fage