1.创建索引
create index PENALTIES_AMOUNT on penalties(amount);
删除： drop index PENALTIES_AMOUNT;
2.创建索引
create view number_sets (matchno,difference) as select matchno,abs(won-lost) from matches;
删除： drop view number_sets;
使用方法:
select * from number_sets;
3.对用户限制在某个表操作
grant select ,update on players to dinnery